Chapter 1 Cellular control

Question 1

What is a mutation?

Answer 1

An unpredictable random change to genetic material. Some involve changes to structure or number of chromosomes.

Question 2

When do mutations arise?

Answer 2

They can occur spontaneously during transcription during DNA replication before cell division. Some chemicals such as tar in tobacco and ionising radiation are also mutagenic (cause mutations).

Question 3

What are consequences of mutations?

Answer 3

• Mutations can be associated with development of cancerous tumors
• Mutation associated with meiosis and gamete formation can affect protein production and function in offspring.
• Mutations can be advantageous, e.g. antibiotic resistance

Question 4

What are the 3 types of mutation?

Answer 4

• Point/ substitution
• Insertion
• Deletion

Question 5

What is a point mutation?

Answer 5

swapping one base pair with another

Question 6

What are the 3 types of point mutation?

Answer 6

• Silent: A mutation that codes for the same amino acid (degenerate)
• Missense: Causes a change to the base triplet sequence which leads to a change in the amino acid sequence, which may lead to a change in the tertiary structure of a protein
• Nonsense: Causes an alteration that leads to a base triplet becoming a termination triplet, resulting in a shortened protein

Question 7

What are insertion mutations?

Answer 7

Addition of a base pair. This causes a frameshift.

Question 8

What are deletion mutations?

Answer 8

Loss of a base pair. This causes a frameshift

Question 9

What is the preferred substrate in E coli?

Answer 9

glucose

Question 10

What happens when glucose is not present but lactose is?

Answer 10

• lactose enters the cell by diffusion
• lactose binds to the repressor protein, causing a conformational change, preventing it from binding to the operator region
• RNA polymerase can bind to the promotor region and transcribe the structural genes into mRNA
• B-galactosidase and lactose permease are synthesised to break down lactose into glucose and galactose

Question 11

What is an operon?

Answer 11

A group of genes that function as a single transcription unit.

Question 12

What is a regulatory gene in the Lac operon?

Answer 12

Codes for a repressor protein (LacI) which switches off/ deactivates genes. The repressor molecule can bind to the operator region.

Question 13

What is the promoter region?

Answer 13

RNA polymerase binds here to begin transcription of the structural genes into mRNA.

Question 14

What is the operator region?

Answer 14

If the repressor molecule has bound to this region, RNA polymerase cannot bind to the promotor.

Question 15

What are structural genes?

Answer 15

Code for the desired proteins (enzymes). LacZ (B-galactosidase) and LacY (lactose permease)

Question 16

How many base pairs does the lac operon consist of?

Answer 16

6000

Question 17

What are introns?

Answer 17

non-coding regions of DNA that are not expressed

Question 18

What are exons?

Answer 18

coding/ expressed regions of DNA

Question 19

What is involved in post-transcriptional gene regulation?

Answer 19

All DNA of a gene is transcribed to form primary mRNA. Primary mRNA is spliced meaning the introns are removed and remaining exon are joined together. The introns can form short non-coding lengths of RNA.

Question 20

What enzyme catalyses splicing?

Answer 20

spliceosome/ endonuclease enzyme

Question 21

What is post-translational gene regulation?

Answer 21

Involves modification and activation of proteins, often by phosphorylation.

Question 22

What is the role of cAMP in activating proteins?

Answer 22

cAMP is a second messenger that activates protein kinase which catalyses the phosphorylation of proteins by hydrolysing ATP into ADP and Pi. These activated proteins can carry out metabolic reactions or act as a transcription factor.

Question 23

What is a homeotic mutation?

Answer 23

Mutation of a hox gene that results in body parts developing in the wrong place on the body.

Question 24

What is the homeotic gene?

Answer 24

The gene that regulates morphogenesis, determining the body plan of an organism.

Question 25

What is the homeobox gene?

Answer 25

A section of the homeotic gene that act as a regulatory gene and contain 180 base pairs, coding for a sequence of 60 amino acids (homeodomain sequence).

Question 26

How are hox genes expressed?

Answer 26

Along the anterior-posterior axis in spatial and temporal order (colinearity).

Question 27

What are hox genes?

Answer 27

Homeobox genes that are only found in animals, expressed in early embryonic development.

Question 28

What is the homeodomain?

Answer 28

60-amino acid sequence that folds into an H-T-H shape consisting of 3 a-helices, 2 of which are connected by a turn. It can act as a transcription factor and bind to DNA to regulate transcription by recognising the TATA sequence of a gene which is then transcribed.

Question 29

What is the process of apoptosis?

Answer 29

1. Enzymes break down cytoskeleton
2. Cytoplasm becomes dense and tightly packed with organelles
3. Small protrusions called blebs form on the cell surface membrane
4. Chromatin condenses, nuclear envelope breaks and DNA breaks into fragments
5. Cell breaks into vesicles that are ingested by phagocytic cells so cell debris doesn’t damage other cells

Question 30

What is apoptosis?

Answer 30

programmed cell death

Question 31

How many times can a cell divide before apoptosis?

Answer 31

50 (hayflick constant)

Question 32

What is the role of mitosis during development?

Answer 32

Mitosis occurs at a faster rate than apoptosis as the organism grows