8. Cellular Control

Question 1

What is a gene mutation?

Answer 1

A random change to the genetic material.

Question 2

What are the two types of mutations?

Answer 2

Point mutation- one base pair replaces (is substituted for) another.
Insertion or deletion (indel)- one or more nucleotides are inserted or deleted from a length of DNA.
These may cause a frameshift.

Question 3

What are the types of point mutations?

Answer 3

Silent, missense and nonsense

Question 4

What are the types of indel mutations?

Answer 4

Insert and deletion and expanding triple nucleotide repeats.

Question 5

What are silent mutations?

Answer 5

When there is a change to a base triplet but it still codes for the same amino acid.
Therefore, the primary and tertiary structure remains the same.

Question 6

What are missense mutations?

Answer 6

A change in the base triplet sequence leads to a different amino acid codon.
The alteration to the primary structure leads to a change to the tertiary structure of the protein.

Question 7

What is caused by missense mutations?

Answer 7

Sickle cell anaemia
The amino acid valine, instead of glutamic acid is produced.
Deoxygenated haemoglobin crystallises, causing erythrocytes to become sickle-shaped, blocking the arteries.

Question 8

What is a nonsense mutation?

Answer 8

A change in one of the bases means that the triplet changes into a stop codon.
The process of translation stops altogether before the protein is formed.
If a protein is truncated (too short) it can become degraded and cause genetic diseases such as muscular dystrophy.

Question 9

How do insertion or deletion mutations work?

Answer 9

If nucleotide base pairs are inserted or deleted, it causes a frameshift.
The primary sequence of the protein, and the tertiary structure, is altered.
The protein will no longer be able to carry out its normal function.

Question 10

How do Expanding triple nucleotide repeats mutations work?

Answer 10

The number of repeating triplets in a gene increases.

Huntington disease results from an expanding triple nucleotide repeat.

Question 11

How are genes regulated in Prokaryotes?

Answer 11

Using the lac operon

Question 12

What is the structure of the lac operon?

Answer 12

Consists of a length of DNA containing…
The regulatory gene
Control sites (Operator region and Promoter region)
Structural genes (lacZ and lacY)

Question 13

How does the lac operon function when not enough lactose is present?

Answer 13

The regulatory gene codes for a repressor protein
The repressor protein binds to the operator.
This prevents RNA polymerase from binding to the promoter region.
This prevents lacZ and lacY from being transcribed.
Enzymes for lactose metabolism are not made.

Question 14

How does the lac operon function when lactose is present?

Answer 14

Lactose binds to the repressor protein molecules.
This alters the shape of the repressor, preventing it from binding to the operator.
The RNA polymerase enzyme can then bind to the promoter region and begin transcribing the structural genes into mRNA.
This will then be translated into the two enzymes.

Question 15

What is lactose used for?

Answer 15

Lactose induces the production of two enzymes…
Lactose permease- allows lactose to enter bacterial cells.
Β-galactosidase- hydrolyses lactose to glucose and galactose.

Question 16

How is gene expression regulated in eukaryotic cells?

Answer 16

Pre-transcriptional…
Transcription factors
Post-transcriptional…
Introns and exons, phosphorylation of enzymes.

Question 17

What are hox genes?

Answer 17

Type of homeobox genes only found in animals

In mammals and tetrapods there are four clusters each containing up to 10 genes.

Question 18

How are Hox genes used in embryonic development?

Answer 18

They are expressed in order along the anterior-posterior axis of the developing embryo.
They follow the rules of colinearity.

Question 19

What is colinearity?

Answer 19

When the spatial and temporal order of gene expressions corresponds to the development of body parts.
Spatial- Where genes are expressed (left to right)
Temporal- When each gene is switched on.

Question 20

What may a mutation in hox genes cause?

Answer 20

A mutation could result in body parts developing in the wrong place on the body.

Question 21

What is Apoptosis?

Answer 21

Programmed cell death.

An active process that requires energy.

Question 22

What is the sequence of events during apoptosis?

Answer 22

1. Enzymes break down the cell cytoskeleton.
2. The cytoplasm becomes dense with organelles.
3. The cell surface membrane forms protrusions called blebs.
4. The nuclear envelope and DNA breaks down.
5. The cell breaks into vesicles (apoptotic bodies) that are ingested by phagocytic cells.

Question 23

What is the function of nitric oxide in apoptosis?

Answer 23

Makes the inner mitochondrial membrane more permeable to hydrogen ions, dissipating the proton gradient.

Question 24

What are the functions of apoptosis?

Answer 24

Prevent the excessive spread of plants, separation of digits in limb development, remove harmful or ineffective cells, balance the number of cells in the body.

Question 25

What is the lifespan of erythrocytes?

Answer 25

120 days

Question 26

What happens if there are too many cells?

Answer 26

Causes tumours

Question 27

What happens if there are not enough cells?

Answer 27

Causes cell loss and degradation

Question 28

What are transcription factors?

Answer 28

Short non-coding pieces of RNA, that act within the cell’s nucleus to control which genes in a cell are turned on or off.

Question 29

What are introns?

Answer 29

Non-coding regions of DNA which are not expressed.

Question 30

What are exons?

Answer 30

Coding and expressed regions of DNA.

Question 31

What is primary mRNA?

Answer 31

A length of mRNA that both introns and exons are transcribed onto.
The introns corresponding to the DNA introns are removed.
The remaining mRNA exons are joined together.

Question 32

What enzymes are involved in the removal of introns and exons?

Answer 32

Endonuclease enzymes

Question 33

What is post-translational level of gene regulation?

Answer 33

Means after the protein has been made.

Involves the activation of proteins through phosphorylation.

Question 34

What are the stages of post-translational level of gene regulation?

Answer 34

1. A signalling molecule binds to the receptor, causing a conformational change.
2. This activates a G protein.
3. The activates adenyl cyclase.
4. This catalysis the formation of cyclic AMP from ATP.
5. cAMP activates PKA (protein kinase A)
6. This catalysis the phosphorylation of proteins and hydrolyses ATP in the process.
7. This enters the nucleus and acts as a transcription factor.

Question 35

What are homeotic genes?

Answer 35

Genes involved in controlling the anatomical development of an organism.

Question 36

What are homeobox genes?

Answer 36

Type of homeotic gene found only in plants, animals, and fungi.
Within each homeobox gene is a homeobox sequence.

Question 37

How long is a homeobox sequence?

Answer 37

A stretch of 180 DNA base pairs.

This encodes for a 60-amino acid sequence called a homeodomain sequence.

Question 38

What is a homeodomain sequence?

Answer 38

They act as transcription factors and fold into a specific shape and bind to DNA regulating the transcription of genes.

Question 39

What is the structure of a homeodomain sequence?

Answer 39

Contains a structure called H-T-H which consists of two alpha helices connected to one turn.

Question 40

What are the different levels of homeotic genes (from broadest to most specific)?

Answer 40

Homeotic Genes, Homeobox Genes, Homeobox sequence, Homeodomain sequence, H-T-H