Module 6.1.1 Cellular Control

Question 1

Define a mutation and state its possible effects (3)

Answer 1

• A mutation is a change in DNA that can result in a non-functioning protein.
• Some mutations may be beneficial, giving an advantage such as antibiotic resistance.
• All alleles of a gene arise from mutations.

Question 2

Describe gene mutations and their effects (6)

Answer 2

• A gene mutation is a change in the base sequence of DNA, often occurring during replication.
• This may alter the amino acid sequence, changing protein folding and shape.
• Changes in the tertiary structure can create a non-functioning protein.
• Mutations can be beneficial, neutral, or harmful.
• Silent mutations occur when the genetic code’s degeneracy means the same amino acid is coded for.
• Mutations may involve base deletion, insertion, or substitution

Question 3

Explain the effect of base deletions and insertions (2)

Answer 3

• They cause a frameshift, altering all subsequent codons.
• This can change many amino acids, producing a faulty protein

Question 4

Explain the role of transcription factors in eukaryotes (4)

Answer 4

• Transcription factors are proteins that move from the cytoplasm into the nucleus.
• They bind to specific base sequences on DNA to initiate transcription.
• Without them, genes remain inactive and proteins are not made.
• An example is oestrogen, which binds to a receptor on a transcription factor, changing its shape so it can bind to DNA and begin transcription

Question 5

Describe the lac operon in E. coli and its regulation (6)

Answer 5

• The lac operon contains three structural genes (lacZ, lacY, lacA) for lactose digestion. Lactose is a disaccharide sugar found in milk, formed by the condensation of glucose and galactose monomers
• Without lactose, a repressor protein binds to the operator, preventing RNA polymerase binding to the promoter.
• When lactose is present, it binds to the repressor, changing its shape so it cannot bind to the operator.
• RNA polymerase can then bind to the promoter, and the genes are transcribed.
• Glucose is preferred as an energy source, so transcription increases when glucose is absent.
• cAMP binds to CRP, increasing transcription rate when glucose levels are low.

Question 6

Explain mRNA modification after transcription (4)

Answer 6

• Pre-mRNA contains introns and exons.
• Introns are removed by the spliceosome in a process called splicing.
• Exons may be rearranged or removed in alternative splicing to produce different proteins.
• The final product is mature mRNA, which can be translated into protein.

Question 7

Explain post-translational changes in proteins (3)

Answer 7

• Proteins may have non-protein groups such as lipids or carbohydrates added.
• They are folded into a 3D shape in the Golgi apparatus.
• Some are made inactive and activated later by phosphorylation.

Question 8

Define homeobox genes and explain their importance (4)

Answer 8

• Homeobox genes are sequences of DNA that code for proteins acting as transcription factors.
• These transcription factors regulate structural genes that control body formation during early embryonic development.
• The sequences are 180 base pairs long and code for a homeodomain region on the protein that binds to DNA.
• They are highly conserved in plants, animals, and fungi, and mutations are often lethal

Question 9

Describe the role and organisation of Hox genes (4)

Answer 9

• Hox genes are a type of homeobox gene found only in animals.
• They determine the body plan, ensuring correct positioning of body parts such as arms, legs, and wings.
• The order of Hox genes in DNA matches the order of expression along the body axis.
• Many animals have segmented bodies, such as insect body parts, worm rings, or vertebrae in vertebrates

Question 10

State the role of mitosis in body development (3)

Answer 10

• Mitosis increases the number of cells, allowing for growth and repair.
• The cell cycle ensures cells are only produced when needed, conserving energy and preventing tumour formation.
• Proto-oncogenes initiate the cell cycle, while tumour suppressor genes stop it when appropriate.

Question 11

State the role of apoptosis in body development (3)

Answer 11

• Apoptosis is programmed cell death, removing unwanted, damaged, or old cells.
• If a cell is faulty or too old to function, apoptosis destroys it and recycles its resources.
• It works alongside mitosis to shape tissues and maintain healthy cell populations.

Question 12

Explain how mitosis and apoptosis are regulated (3)

Answer 12

• Both processes respond to internal signals, such as hormones and psychological stress.
• They also respond to external factors, including changes in temperature.
• Hox genes regulate both processes, with the highest activity during growth and development