HS-LS1-1: Explaining How DNA Structure Determines Protein Structure
In plain English: HS-LS1-1 is the NGSS high school performance expectation that asks students to construct an explanation, based on evidence, of how the base sequence of DNA sets the amino acid sequence and shape of proteins, and how those proteins let systems of specialized cells carry out the functions of life. It is usually taught in Biology.
Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells.
Assessment Boundary: Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis.
Next Generation Science Standards · Disciplinary Core Idea: From Molecules to Organisms: Structures and Processes · Official standard
Students construct an explanation, based on evidence, of a chain of cause and effect: the order of bases in a gene sets the order of amino acids in a protein, the order of amino acids sets the shape the chain folds into, and the shape lets the protein do its job. They also explain why cells that carry the same DNA can become specialized: each kind of cell uses a different set of genes, so it makes a different set of proteins, and specialized cells work together in systems. Students read short genes with a codon key, predict what base changes do to a protein, and build claim-evidence-reasoning explanations from invented yeast and plant data and from classic gene-transfer evidence.
HS-LS1-1 has no Clarification Statement. The official Assessment Boundary reads: "Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis." So students always receive a codon key and never memorize it, they are not asked to name cell types, tissues or body systems, and they do not identify real proteins by structure or job. The steps and enzymes that copy and read a gene (the biochemistry of protein synthesis, including how ribosomes and transfer RNA work) are beyond this standard; the lesson only says that the gene's sequence is copied into a messenger molecule (mRNA) that is read three bases at a time.
Learning Objectives
By the end of this lesson, students will be able to:
Describe DNA as two strands of bases held in pairs (A with T, C with G) and use base pairing to predict a partner strand and base percentages
Use a codon key to turn the base sequence of a gene into an amino acid sequence, and explain why the order of bases sets the order of amino acids
Predict and explain how a substitution, insertion or deletion can change a protein's amino acid sequence, its shape and its ability to do its job
Explain why cells with identical DNA make different proteins and how those specialized cells work together in systems
Construct a claim-evidence-reasoning explanation from data that links a gene, its protein and a function
Prior Knowledge Required
Students should already be comfortable with:
Changes to genes (mutations) can change proteins and traits MS-LS3-1
Cells and their parts carry out the functions of life MS-LS1-2
The body is a system of interacting subsystems made of groups of cells MS-LS1-3
Molecules are atoms joined in a particular arrangement MS-PS1-1
Write two sentences on the board: "the dog bit the man" and "the man bit the dog." Point out that they use exactly the same letters. Then show the prompt.
Warm-Up Prompt
"DNA uses only four chemical letters: A, T, C and G. Your cells make thousands of different proteins, and each one has a different job. How could an alphabet of four letters hold the instructions for all of them? What would happen if one letter in an instruction changed?"
Collect ideas without correcting them. Guide students to the idea that order carries the information, as in the two sentences. Tell students that proteins are built from 20 kinds of amino acids, and leave a second question on the board for later: how many letters of DNA would it take to name one amino acid? Keep the question "what if one letter changed?" on the board for the end of the lesson.
Direct Instruction20 minutes
Part 1: The structure of DNA. Show a model or image of the double helix, then Diagram 1. Stress three structural points:
Two strands: each strand is a long chain of units, and each unit carries one of four bases, A, T, C or G. The order of bases along a strand is the information.
Base pairing: the strands are held together by base pairs, and A always pairs with T while C always pairs with G. So each strand fixes the order of bases on its partner, which is how the information can be copied exactly.
Genes: a gene is a stretch of DNA whose base order is the instruction for one protein. A protein is a chain of amino acids, and its job depends on its shape.
Part 2: From base order to protein. Explain the model in Diagram 1 at the level the standard asks for: the cell copies the base sequence of a gene into a messenger molecule, mRNA, in which U takes the place of T, and the mRNA is read three bases at a time. Each three-base codon names one amino acid, and a stop codon ends the chain. Hand out the codon key below and tell students they will always have it; nobody memorizes it. (The key lists only the codons used in this lesson. The full genetic code has 64 codons.)
Codon key for this lesson (mRNA codons; for a DNA coding strand, read T as U)
Amino acid
mRNA codons
Ala (alanine)
GCA, GCC, GCU
Arg (arginine)
AGA, CGU
Asn (asparagine)
AAU
Asp (aspartic acid)
GAU
Cys (cysteine)
UGC
Gln (glutamine)
CAG
Glu (glutamic acid)
GAA, GAG
Gly (glycine)
GGA, GGC, GGU
His (histidine)
CAC, CAU
Ile (isoleucine)
AUC
Lys (lysine)
AAA, AAG
Met (methionine), also the start signal
AUG
Phe (phenylalanine)
UUC, UUU
Pro (proline)
CCA, CCG
Ser (serine)
AGC, UCA
Thr (threonine)
ACC, ACU
Trp (tryptophan)
UGG
Tyr (tyrosine)
UAC, UAU
Val (valine)
GUA, GUG, GUU
Stop (no amino acid; the chain ends)
UAA, UAG, UGA
DNA structure: predicting the partner strand
One strand of a DNA segment reads TACGGATTC. Write the partner strand.
A DNA sample from a pine tree is 31% adenine (A) (invented but realistic value). Predict the percent of T, G and C.
Result: Every A pairs with a T, so T = 31%. G and C share the rest: 100 - 62 = 38%, so G = 19% and C = 19%. Measurements like these from many species (A ≈ T and G ≈ C) are evidence for the paired-strand model.
Gene to amino acid sequence
A gene's coding strand reads ATG GCT AAA GAA TGG TAA. Use the codon key to find the amino acid sequence.
Result: mRNA codons: AUG GCU AAA GAA UGG UAA. Amino acids: Met-Ala-Lys-Glu-Trp, then stop. Five amino acids, in the order set by the bases.
Substitution: one base changes
Two versions of the same gene differ from ATG GCT AAA GAA TGG TAA by one base each: version 1 has GCA in place of GCT, and version 2 has GTA in place of GAA.
Result: Version 1: GCA still codes for Ala, so the protein is unchanged (Met-Ala-Lys-Glu-Trp). Version 2: GUA codes for Val, so the chain is Met-Ala-Lys-Val-Trp. One different amino acid can change how the chain folds, and so what the protein can do.
Insertion: the reading frame shifts
An extra G is inserted right after the first codon: ATG GGC TAA AGA ATG GTA A.
Result: Codons are now AUG GGC UAA ... so the chain is Met-Gly, then stop. Every codon after the insertion is read in a new frame, and here a stop codon appears at once: the protein is two amino acids long instead of five.
Part 3: Same DNA, different cells. Nearly every cell in a multicellular organism carries the same genes. Cells become specialized because each kind uses (expresses) a different set of those genes, so each makes a different set of proteins. The proteins let each cell do its part, and specialized cells work together in systems that carry out the essential functions of life, such as moving, taking in nutrients or responding to signals. Share one piece of evidence that specialized cells keep all their genes: in 1996 scientists moved the nucleus of a specialized body cell from an adult sheep into an egg cell whose own nucleus had been removed, and the egg developed into a whole lamb (Dolly). Return to Diagram 1 and ask students to trace one arrow at a time from bases to a working cell.
Guided Practice15 minutes
Pairs study invented data from a yeast investigation. The yeast use one enzyme to break down a sugar in their food, and the gene for that enzyme was sequenced in five strains. Enzyme activity was measured in each strain and compared with the normal strain. Show the table and Diagram 2.
Enzyme gene, protein and activity in five yeast strains (invented data)
Strain
Change in the gene
Change in the enzyme
Activity (% of normal)
Growth on the sugar
1
None (normal gene)
None
100
Grows well
2
One base substituted
None: the new codon names the same amino acid
98
Grows well
3
One base substituted
One amino acid replaced
12
Grows slowly
4
One base inserted near the start
Chain ends after 9 amino acids
0
No growth
5
Strain 4 cells given a normal copy of the gene
Normal enzyme made
95
Grows well
Pairs write a claim, evidence and reasoning (CER) explanation for the question "How does the gene determine whether a yeast strain can use the sugar?" Prompt with these questions:
Which two strains show that a base change does not always change the protein? (Strains 1 and 2: activity 100% and 98%.)
Which strain gives the strongest evidence that the gene, not something else about the strain, controls the enzyme? (Strain 5: adding a normal copy of the gene to strain 4 cells raised activity from 0% to 95%.)
Why would one replaced amino acid in strain 3 lower activity to 12%? (A different amino acid can change the way the chain folds, and the enzyme's shape is what lets it work.)
What would you need to know to be more confident? (Several trials per strain, and whether the strains were grown in the same conditions.)
Model the reasoning sentence: "Because the base sequence sets the amino acid sequence, and the amino acid sequence sets the enzyme's shape, a change in the gene can change or stop the enzyme's function."
Independent Practice10-15 minutes
Students work alone on two versions of a short gene. Normal: ATG TTC GGA CAT AAG TGA. Changed: the 7th base is T instead of G. (1) Translate both with the codon key. (Normal: Met-Phe-Gly-His-Lys. Changed: the third codon becomes UGA, a stop codon, so the chain is only Met-Phe.) (2) Write a two-sentence prediction of how the change affects the protein's ability to do its job, and a reasoning sentence that uses the word "shape." Collect the work to check for the errors listed in the assessment guidance.
Closure5 minutes
Exit ticket: (1) One DNA strand reads GATTACA. Write its partner strand. (CTAATGT.) (2) Finish the chain: base sequence, then amino acid sequence, then ______, then function. (Shape.) (3) In one sentence, explain how two cells with the same DNA can do different jobs. Then answer the warm-up question on the board: what happens if one letter changes?
Differentiation Strategies
For Struggling Students
Give genes with the codons already separated by spaces, and a codon key with the rows highlighted in the same colors as the beads
Use a three-column organizer: "gene changes," "protein changes," "job changes," and fill it in for each strain in the yeast data
Provide sentence starters for CER: "The data show...," "This supports the claim because..."
For Advanced Students
Ask why a deletion of three bases in a row usually does less damage than a deletion of one base, and test the idea on a gene card
Ask students to explain why a change in the first codon position more often changes the amino acid than a change in the third position, using the codon key
Ask how scientists could use a gene from one species to make a protein in another species, and what that shows about the genetic code (extends toward HS-LS3-1)
Assessment Guidance
What to Look For
Strong explanations follow the full chain in order: base sequence, then amino acid sequence, then shape, then function, and they cite specific data (a strain, a percent, a translated sequence) as evidence. Watch for these errors: pairing A with G or C with T; reading codons from the wrong starting point; treating every mutation as harmful (silent changes exist); and explanations of specialized cells that never say which genes a cell uses. The codon key is always provided, and students should not be graded on naming cell types, body systems, real proteins or the steps of protein synthesis.
02
Classroom Activities
3 Activities
1
Build a Protein from a Gene
25 minPairs
Pairs translate a gene card with the codon key, build the amino acid chain as a bead model, then apply a mutation card and rebuild. Comparing the four cards gives the class evidence for how different base changes affect a protein.
Materials
One gene card per pair (cards A, B, C and D, below), each with a matching mutation card
The codon key from Direct Instruction
A pipe cleaner and pony beads in 8 colors, one color per amino acid used on the cards (a color chart on the board)
A class results table on the board
The Four Gene Cards
Card A: ATG GGA TGG AAA GCT TAA. Mutation card: the 15th base changes from T to A.
Card B: ATG CAT GAA TTC GGC TAG. Mutation card: the 8th base changes from A to T.
Card C: ATG AAG TGG CCA GAT TGA. Mutation card: the 9th base changes from G to A.
Card D: ATG ATC CGT AAG GAA TAC TAA. Mutation card: an extra C is inserted after the 4th base.
Procedure
Split the gene into codons, change T to U, and look up each codon in the key
Thread one bead per amino acid onto the pipe cleaner, in order, and stop at the stop codon
Apply the mutation card to the gene, translate again and build a second chain
Record both chains on the class table and label the change: no change to the protein, one amino acid changed, chain ends early, or reading frame shifted
Answer Key for the Teacher
Card A: Met-Gly-Trp-Lys-Ala; after the mutation, Met-Gly-Trp-Lys-Ala.
Card B: Met-His-Glu-Phe-Gly; after the mutation, Met-His-Val-Phe-Gly.
Card C: Met-Lys-Trp-Pro-Asp; after the mutation, Met-Lys.
Card D: Met-Ile-Arg-Lys-Glu-Tyr; after the mutation, Met-Thr-Pro.
So card A shows a change with no effect on the protein, card B one replaced amino acid, card C a chain that ends early, and card D a shifted reading frame that also ends early.
Discussion Questions
Which card changed a base without changing the protein? How is that possible? (Card A: GCU and GCA both code for Ala.)
Cards B and D both involve one base. Why is the effect of D so much larger?
The bead model shows the order of amino acids. What does it leave out about a real protein? (The folded shape, which is what lets the protein work.)
Use the class table to support a claim about how the base sequence determines the protein.
Variation: Paper Strips
Without beads, pairs write each amino acid on a paper strip in a different color and tape the strips into a chain.
2
Same Genes, Different Cells
20 minSmall groups (4)
Each group models a small organism in which every cell carries the same 8 genes. Groups decide which genes each specialized cell uses, then connect the cells into a system that carries out one function, and test what happens when one gene is changed.
Materials
For each group: 4 identical "genome" sheets listing 8 genes, each with the protein it codes for and what that protein does (for example, "Gene 3: a protein that shortens the cell when a signal arrives")
4 cell-role cards: a cell that receives a signal from outside, a cell that passes a signal on, a cell that shortens (contracts), and a cell that builds a tough outer covering
Sticky notes and a sheet of poster paper
Procedure
Each group member takes one cell-role card and one genome sheet, and circles the genes that cell must use to do its role. All four sheets start identical
Tape the four sheets onto the poster and draw arrows showing how the cells work together as a system so the organism can pull away when something touches it
Draw a "mutation card" from the teacher that changes one gene so its protein can no longer fold correctly. Mark which cells use that gene and predict what happens to the system
Discussion Questions
All four cells carry all 8 genes. What makes them different from one another?
Your mutation changed one gene. Why might it affect only one kind of cell, yet still stop the whole system from working?
What evidence from Direct Instruction shows that a specialized cell still carries every gene?
Modification for Distance Learning
Share the genome sheet and role cards as a slide. Each student builds one cell on a shared slide, and the group connects the cells with arrows during a video call.
3
Weigh the Evidence
20 minSmall groups (3-4)
Groups sort six evidence cards, decide which ones support the claim "the base sequence of DNA determines the structure of proteins, which carry out the functions of cells," rank the strongest three, and write one CER paragraph.
The Six Evidence Cards
Card 1: In DNA from four species (invented values), the percent of A and T are 29% and 29%, 31% and 31%, 25% and 25%, and 22% and 22%, and G equals C in every sample
Card 2: A gene from fireflies was placed in tobacco plants in the 1980s, and the plants made the firefly protein and glowed faintly when they were given the chemical that protein acts on
Card 3: Pea plants with one base change in a gene for a growth enzyme are short; plants with the normal gene are tall (invented numbers: 12% vs 100% enzyme activity)
Card 4: Cells need water to survive
Card 5: Two yeast strains with the same gene sequence make enzymes with the same amino acid sequence and the same activity
Card 6: A lamb developed from an egg cell given the nucleus of a specialized adult sheep cell
Procedure
Sort the cards into "supports the claim," "supports a different claim" and "not relevant"
Rank the three strongest cards and explain the ranking in one sentence each
Write a CER paragraph that uses at least two cards and states the reasoning chain: bases, amino acids, shape, function
Discussion Questions
Card 1 is about DNA structure, not proteins. How does it still support part of the explanation? (Every sample has A equal to T and G equal to C, which fits the base-pairing model that lets the sequence be copied.)
Card 6 supports a different part of the claim. Which part?
Why is Card 4 true but not evidence for this claim?
Modification for Distance Learning
Put the cards on a shared slide. Groups drag each card into one of three columns and type their CER paragraph under the columns.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Model from Gene to Working Protein
The top band shows a stretch of a gene with its partner strand (A pairs with T, C with G). The gene's base sequence is copied into mRNA and read three bases at a time; each codon names one amino acid. The order of amino acids sets how the chain folds, and the folded shape lets the protein do its job in specialized cells that work together in systems. The steps that copy and read the gene are beyond this standard.
Diagram 2: Evidence from Five Yeast Strains
Bars are drawn to scale for the invented data in Guided Practice. A base change that keeps the same amino acid (strain 2) leaves activity near normal, one replaced amino acid (strain 3) lowers it sharply, and an insertion (strain 4) stops it. Giving strain 4 cells a normal copy of the gene (strain 5) restores activity.
04
Homework Assignment
~30 min
HS-LS1-1 Homework: From DNA to Protein Function
Directions: Use the codon key from the lesson for every translation. Write codons with spaces between them and show your work. For every explanation, give a claim, the evidence you used and your reasoning. All data sets are invented for practice.
Part 1: DNA Structure (Problems 1-2)
One strand of a DNA segment reads CGTTAGCATGGA. (a) Write the partner strand. (b) Count the A, T, G and C bases in the whole double-stranded segment (both strands, 24 bases) and write each as a percent. (c) Explain how your percents show the base-pairing rule.
Researchers measured the base percents in four DNA samples (invented data). Sample W: A 27%, T 27%, G 23%, C 23%. Sample X: A 33%, T 33%, G 17%, C 17%. Sample Y: A 25%, T 32%, G 24%, C 19%. Sample Z: A 20%, T 20%, G 30%, C 30%. (a) Which sample does not fit the model of two paired strands? (b) Use the pairing rule to explain your choice. (c) Propose one explanation for that sample that fits the evidence.
Part 2: From Gene to Protein (Problems 3-4)
A gene's coding strand reads ATG GAT TGC CAG AAT GGT TGA. (a) Write the mRNA codons and the amino acid sequence. (b) In a second version the 12th base is T instead of G. Translate it and describe the change to the protein. (c) In a third version the 5th base (A) is deleted. Translate as far as the bases allow and explain why the effect is larger than in (b).
The coding part of a gene, from the start codon through the stop codon, is 1,500 bases long. (a) How many codons does it contain? (b) How many amino acids are in the protein? (c) A mutation deletes three bases in a row (exactly one codon) from the middle of this gene. How many amino acids does the protein now have, and why are the amino acids after the deletion unchanged?
Part 3: Constructing Explanations (Problems 5-6)
In a set of invented data, sunflowers with a normal growth gene reach a mean height of 180 cm and make a growth enzyme with 100% activity. Sunflowers with one base substituted in that gene reach a mean of 45 cm, and their enzyme has 20% activity. The substitution replaces one amino acid. (a) By what percent is the mean height of the changed plants lower than that of the normal plants? (b) Write a CER explanation of how one base change can make a plant short. Your reasoning must connect bases, amino acids, protein shape and function.
A cell from the lining of a person's intestine and a cell from the same person's skin have the same DNA, yet they make very different proteins. (a) Explain how this is possible. (b) Describe one piece of evidence that specialized body cells keep all their genes. (c) A gene used only by the intestine cells is changed so its protein cannot fold properly. Predict how this could affect the whole organism, and explain why the skin cells are not affected.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
No Credit (0 pts)
Base Pairing
Partner strands and percents correct; pairing rule used as evidence
One pairing or counting error
Pairing rule not used or incorrect
Translation
Codons read in the right frame with the key; changes to the protein described correctly
Correct method with one lookup error
Codons misread or key not used
Explanation
Claim, specific evidence and reasoning that links bases, amino acids, shape and function
Claim and evidence given but the chain of reasoning is incomplete
No claim or no evidence
Specialized Cells
Same genes, different genes used; evidence cited; effect on the system predicted
Idea correct but evidence or prediction missing
Says cells have different DNA
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Answer each question, then open the explanation to check your reasoning. The running score counts correct answers, and Reset quiz starts over. Use the codon key from the lesson for every translation. All data are invented unless the question names a real experiment.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which statement describes how the two strands of a DNA molecule are held together?
Answer: A
Base pairing is always A with T and C with G, so one strand sets the sequence of its partner. Choice B uses the wrong pairs. Choice C would make the two strands identical, but they are complementary. Choice D confuses DNA with protein: amino acids are not part of DNA.
Question 2 of 20 · Multiple Choice
One DNA strand reads GCATTA. What is its partner strand?
Answer: C
Pair each base: G-C, C-G, A-T, T-A, T-A, A-T, which gives CGTAAT. Choice A repeats the strand instead of pairing it. Choice B writes the strand backward. Choice D uses U, which appears in mRNA, not in DNA.
Question 3 of 20 · Multiple Choice
A DNA sample from a sea star is 22% guanine (G). What percent of its bases are adenine (A)?
Answer: B
G pairs with C, so C is also 22% and G + C = 44%. A and T share the other 56%, so A = 28%. Choice A assumes A equals G. Choice C is G + C, and choice D is A + T together.
Question 4 of 20 · Multiple Choice
The coding part of a gene, from the start codon through the stop codon, is 90 bases long. How many amino acids are in the protein it codes for?
Answer: D
The gene has 90 ÷ 3 = 30 codons. The stop codon ends the chain and adds no amino acid, so the protein has 29. Choice A counts bases, not codons. Choice B counts the stop codon as an amino acid. Choice C reads two bases per codon.
Question 5 of 20 · Multiple Choice
A gene's coding strand reads ATG CCA GAT TTC TAG. Using the codon key, what is the amino acid sequence?
Answer: A
The mRNA codons are AUG CCA GAU UUC UAG: Met, Pro, Asp, Phe, then stop. Choice B reads past the stop codon. Choice C keeps the start codon but then pairs the remaining bases, as if reading the partner strand. Choice D leaves out Met, but AUG is both the start signal and the first amino acid.
Question 6 of 20 · Multiple Choice
Why must each codon be at least three bases long?
Answer: C
With four bases, two-base codons allow only 16 different codons, but proteins use 20 kinds of amino acids; three bases allow 4 × 4 × 4 = 64. Choice A is false: proteins use 20 kinds of amino acids. Choice B is false: DNA has two strands.
Question 7 of 20 · Multiple Choice
A gene contains the codon AAA (Lys). Which single base change would leave the protein unchanged?
Answer: B
AAG also codes for Lys, so the amino acid sequence stays the same. Choice A gives Asn, a different amino acid. Choice C gives Glu. Choice D gives a stop codon, which would end the chain early.
Question 8 of 20 · Multiple Choice
Near the start of a 300-codon gene, one base is deleted. Near the start of a second copy of the gene, one base is substituted and the new codon names a different amino acid. Which prediction is best supported?
Answer: D
Codons are read three bases at a time from a fixed start, so losing one base regroups every later base into new codons. A substitution changes only its own codon. Choice A ignores the frame shift. Choice C is wrong: one amino acid, or a shifted frame, can change the protein's shape.
Question 9 of 20 · Multiple Choice
A student claims "different kinds of cells in your body have different DNA." Which evidence best contradicts the claim?
Answer: A
If a specialized cell had lost the genes other cells use, its nucleus could not direct the development of every kind of cell in a whole tadpole. (John Gurdon did this experiment with frogs in the early 1960s.) Choice B describes a result of specialization, not evidence about the DNA. Choice D is true of most cells but says nothing about whether their DNA differs.
Question 10 of 20 · Multiple Choice
Scientists place a human gene into bacteria, and the bacteria make a protein with the same amino acid sequence as the human protein. What does this evidence best support?
Answer: B
The only instruction the bacteria received was the gene's base sequence, and they made the matching protein, so the sequence carries the information. Choice A is false: the bacteria had to be given the gene. Choice D is contradicted by the result itself.
Question 11 of 20 · Multiple Choice
Invented data for a gene in rice plants: version 1 (normal) gives an enzyme with 100% activity; version 2, with one base changed in the third position of a codon, gives 97%; version 3, with one base changed in the first position of a different codon, gives 15%. Which conclusion is best supported?
Answer: C
Activity near 100% fits a change that left the amino acid sequence the same, and a drop to 15% fits a replaced amino acid that changed how the chain folds. Choice A is contradicted by version 2. Choice B overgeneralizes from one example of each position; third-position changes can change the amino acid too.
Question 12 of 20 · Multiple Choice
A student writes: "A mutation changes the shape of the DNA double helix, so the cell stops working." Which revision best fixes the explanation?
Answer: D
The double helix keeps its overall shape after a base change. What changes is the information: the base order, and so possibly the amino acid order, the protein's shape and its function. Choice B is false: many mutations have no effect on the protein. Choice A has no basis.
Question 13 of 20 · Multiple Choice
In an animal, a group of specialized cells shortens when it receives a signal, which lets the animal pull away from danger. A gene used only by those cells is changed so its protein folds incorrectly. Which prediction best follows from the model?
Answer: A
Only the cells that use the gene depend on its protein, but the system needs every part to work, so one faulty protein in one cell type can stop the system's function. Choice B forgets that other cells do not use that gene. Choice C is wrong because, by the problem, only those cells use it.
Question 14 of 20 · Multiple Choice
A gene codes for a chain of 200 amino acids. The codon for amino acid number 41, UGG (Trp), changes to UAG. What happens to the protein?
Answer: C
UAG is a stop codon, so the chain stops before amino acid 41 and keeps only the first 40. Choice A would be true only if UAG named another amino acid. Choice B misreads the key: only UGG codes for Trp.
Question 15 of 20 · Short Answer
A gene's coding strand reads ATG TGC AAG CCA GGA TAG. Write the mRNA codons and the amino acid sequence. How many amino acids are in the chain?
AUG UGC AAG CCA GGA UAG. The chain is Met-Cys-Lys-Pro-Gly, 5 amino acids. UAG is a stop codon and adds no amino acid.
Question 16 of 20 · Short Answer
A DNA sample from a mushroom is 26% thymine (T) (invented value). Find the percent of each of the other three bases and explain which part of the DNA model you used.
A = 26%, G = 24%, C = 24%. T pairs with A, so A equals T. A + T = 52%, so G + C = 48%, and G pairs with C, so each is 24%. This uses the base-pairing model of two complementary strands.
Question 17 of 20 · Short Answer
Invented data: a mouse strain with one base inserted into a gene for a muscle protein cannot make the complete protein, and the mice tire quickly. When cells of the strain are given a normal copy of the gene in the lab, they make the full protein. Write a CER explanation of how the gene affects the mice.
Claim: the gene's base sequence determines the muscle protein, and without the complete protein the muscle cells cannot do their job. Evidence: the insertion strain lacks the full protein and tires quickly; adding a normal copy restores the full protein. Reasoning: an insertion shifts the reading frame, so the codons after it name the wrong amino acids or a stop codon; the chain cannot fold into its working shape, so the specialized muscle cells, and the system they belong to, cannot work normally.
Question 18 of 20 · Short Answer
The partner strand of a short gene reads TACCGTAAAATT. Write the gene's coding strand, then the mRNA codons, then the amino acid sequence.
Coding strand: ATGGCATTTTAA. mRNA: AUG GCA UUU UAA. Amino acids: Met-Ala-Phe, then stop. Pair each base of the partner strand to get the coding strand, change T to U for the mRNA, and read codons from AUG.
Question 19 of 20 · Short Answer
Explain why changing one amino acid in a protein can stop the protein from working, even though the other amino acids are unchanged.
A protein's job depends on its shape, and its shape depends on how the chain of amino acids folds. The order of amino acids sets that folding, so replacing one amino acid can change the folded shape, and a protein with the wrong shape may no longer fit or act on what it normally works with. Some replacements have little effect, which is why each change must be tested with evidence.
Question 20 of 20 · Short Answer
A student writes: "Liver cells make different proteins from skin cells because liver cells have liver genes and skin cells have skin genes." Critique the explanation and write an improved version.
The error is that both cells carry the same genes; the difference is which genes each cell uses. Evidence: a nucleus from a specialized adult cell can direct the development of a whole animal, so it still holds every gene. Improved version: "Liver and skin cells have the same DNA, but each kind of cell uses a different set of genes, so each makes different proteins, and those proteins let the cells do their specialized jobs."
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-LS1-1 mean?
HS-LS1-1 asks students to explain, using evidence, how the structure of DNA determines the structure of proteins, and how proteins do the work of systems of specialized cells. "HS" is high school, "LS1" is the life science core idea From Molecules to Organisms: Structures and Processes, and 1 is its number. The key idea is a chain: base sequence, amino acid sequence, protein shape, function.
Does HS-LS1-1 include transcription and translation?
Only at the level of the code, not the chemistry. The Assessment Boundary excludes "the biochemistry of protein synthesis." Students can say that a gene is copied into mRNA and read three bases at a time, and use a codon key. The enzymes involved, how ribosomes and transfer RNA work, and RNA processing are beyond this standard.
Do students need to memorize the codon chart for HS-LS1-1?
No. Give students a codon key or chart for every task. The standard assesses reasoning with the code, such as predicting what a base change does, not recall of which codon names which amino acid.
Is HS-LS1-1 taught in Biology?
Yes, it is usually taught in high school Biology or Life Science, often in a unit on DNA and proteins that comes before genetics and inheritance (HS-LS3-1). It builds on middle school ideas about mutations (MS-LS3-1) and cells (MS-LS1-2).
What evidence shows that DNA determines protein structure?
Good classroom evidence includes: genes moved into another species make the same protein there, such as the firefly gene that let tobacco plants glow when they were given the chemical the firefly protein acts on; a single base change that alters one amino acid and changes a protein's activity; frameshift changes that stop a protein from being made; and base-composition data (A equals T, G equals C) that support the paired-strand structure.
Why do cells with the same DNA do different jobs?
Because each kind of cell uses a different set of its genes. A specialized cell makes the proteins its role needs and not the others, even though it carries all the genes. Evidence comes from cloning: the nucleus of a specialized adult cell can direct the development of a whole animal.
What mistakes do students make with HS-LS1-1?
Frequent ones are pairing A with G, starting to read codons at the wrong base, reading past a stop codon, assuming every mutation is harmful, and forgetting that the stop codon adds no amino acid.
Does every mutation change the protein?
No. Several codons can name the same amino acid, so some base substitutions leave the protein unchanged. Others replace one amino acid, which may or may not change the protein's shape, and insertions or deletions of one base shift the reading frame and usually change everything after them.
How can I assess the explanation practice in HS-LS1-1?
Use claim-evidence-reasoning tasks with a short data set: a gene sequence, a change and a measured effect. A strong answer states a claim, cites specific data and gives reasoning that follows the full chain from bases to function. Score the reasoning, not vocabulary about cell types or real protein names, which the boundary excludes.
What comes after HS-LS1-1?
HS-LS1-2 models how specialized cells form tissues, organs and systems. HS-LS3-1 asks questions about how DNA and chromosomes code for traits passed from parents to offspring, and HS-LS3-2 explains how genetic variation arises, including from mutations.
07
Related Standards
6 standards
These standards connect to HS-LS1-1: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-LS3-1Prerequisite
Model why changes to genes may affect proteins and cause harmful, helpful or neutral effects
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