Stem Cells
What is a stem cell?
A cell that can divide and become other cell types.
What is cell specialization (cell differentiation)?
The process where cells become different in structure and function by expressing certain genes.
What is a mutation in DNA?
A change in the DNA sequence.
What does a gene code for?
A gene codes for a protein (or functional RNA) by specifying a sequence of amino acids.
Give one example from the unit that shows the environment affecting gene expression (plant or animal example).
Example: Hydrangea flower color changes with soil pH; Himalayan rabbits’ coat color varies with temperature.
What are the two types of stem cells?
Embryonic stem cells and somatic stem cells.
Give one example of a specialized cell in animals and the specific protein or structure it produces to perform its function.
Example: Red blood cell — makes lots of hemoglobin protein and loses nucleus to carry oxygen.
Define a point mutation and a frameshift mutation in one sentence each.
Point mutation: a single base is substituted; Frameshift: insertion or deletion of a base shifts reading frame.
What is the start codon (name the amino acid it codes for) in DNA terms given the table convention used in the unit? (Answer in DNA codon form.)
The start codon corresponds to Methionine; in DNA codon form used in the unit, start is AUG (codes for Met in the provided table). TAC
Explain how temperature affected the coat color of Himalayan rabbits described in the unit.
The gene producing pigment is inactive above 35∘ C, so warmer central body regions are white; cooler extremities are dark because the gene is active.
Why are embryonic stem cells considered pluripotent? Use the term "pluripotent" in your answer.
Embryonic stem cells are pluripotent because they can develop into almost all cell types in the body.
Explain how turning genes on and off leads to specialization. Include the terms "gene expression" and "protein" in your answer.
Turning genes on/off changes which mRNA and proteins a cell makes; proteins determine the cell’s specialized structure and function.
Which type of point mutation could create a stop codon and halt protein production? Name the type and briefly explain.
Nonsense mutation; it changes a codon to a stop codon, halting translation early.
Using the codon table excerpt from the unit, if the DNA codon is TACTAG, what amino acid is produced? (Answer the amino acid.)
TACTAG codes for Methionine and Isoleucine.
Describe one internal factor and one external factor that can influence cell differentiation.
Internal factor: hormones (signal differentiation); External factor: temperature or pH (environmental cues affecting gene expression).
Explain one potential medical use for stem cells and one ethical concern associated with their use
Medical use: tissue repair or organ regeneration (e.g., replacing damaged heart tissue). Ethical concern: destroying embryos to obtain embryonic stem cells.
How can identical DNA produce different cell types within a multicellular organism? Briefly explain the role of transcription or gene regulation in this process.
Cells with the same DNA become different cell types because gene regulation controls which genes are transcribed into RNA and translated into proteins, so different sets of active genes produce different traits and functions.
Describe what happens to the protein produced by a frameshift mutation and why it often causes major problems.
Frameshift alters the reading frame so every codon after the mutation is changed, often producing a nonfunctional protein.
A DNA sequence changes from TAC|GAA|TGG|AAT|ACG|AAT|GGA|ATA to TAC|GAA|TGG|AAT|TTA|CGA|ATG|GAA|T.
Explain, in simple terms, how this frameshift changes the resulting amino acid sequence.
Adding a T shifts grouping of codons downstream so every amino acid after insertion is likely different, often producing a nonfunctional protein.
Hydrangea flower color can change with soil pH. Explain how this supports the idea that the environment can influence traits (use the term "gene expression" in your answer).
Soil pH alters availability or form of pigments or the expression of pigment-producing genes; plants in different pH produce different pigments/colors.
Describe how the DNA (genome) of a stem cell compares to the DNA (genome) of a specialized cell in the same organism, and explain why stem cells can become many different cell types.
Both have the same complete genome (same DNA sequence). Stem cells can become many cell types because different genes are turned on/off (different gene expression) during differentiation.
A developing embryo produces many cell types — draw the steps showing how a stem cell differentiates into a specialized muscle cell, starting with the gene to the trait.
Steps: (1) Gene activation, (2) Protein Synthesis, (3) Trait Formation (Specialization).
Explain how mutations can be harmful, beneficial, or neutral. Give one short example for each type (one sentence each).
Harmful: mutation disrupts a vital protein (e.g., loss of function causing disease). Beneficial: mutation gives advantage (e.g., antibiotic resistance in bacteria). Neutral: mutation changes DNA but not the amino acid (silent) or affects noncoding region.
Explain how a base substitution (point mutation) might not change the protein at all (use the term "silent mutation") and give a simple example scenario.
A silent mutation changes a base but the new codon still codes for the same amino acid due to redundancy in the genetic code (e.g., if GAAGAA and GAGGAG both code for Glu, changing A to G may not change the amino acid).
A gene is active only at low temperatures and inactive at high temperatures. Predict what would happen to cells in a tissue if the environment temperature increased above the gene's active range, and explain how that could affect the tissue's function.
If temperature rises above the active range, the gene would be turned off in those cells, reducing the protein product; tissue may lose the function that protein provided (e.g., pigment production or enzyme activity), altering the tissue's role.