Regulation of gene expression

Question 1

Phenotype

Answer 1

The observable characteristics of an organism, resulting from interactions between the genotype and environment.

Question 2

Differentiation

Answer 2

Changing patterns of gene expression as cells become specialised.

Question 3

Housekeeping genes

Answer 3

Code for common structural proteins and enzymes (eg. histones, RNA polymerase, tubulin, pyruvate kinase) that are expressed by all different cell types.

Question 4

Cell memory

Answer 4

The ability for a cell to maintain its morphology and pattern of gene expression.

Question 5

Regulation of gene expression

Answer 5

Control of transcription is the predominant level of regulation of gene expression.

Question 6

Transcriptional unit

Answer 6

Composed of:

• structural information coding for a protein
• regulatory sequences giving instructions for expression

Question 7

Promoters

Answer 7

5’ regulatory sequences which control the initiation of transcription.

Question 8

General transcription factors

Answer 8

Gene-regulatory proteins which recognise and bind to gene promoter sites, where they recruit RNA polymerase. This allows a basal level of transcription.

Question 9

Enhancers

Answer 9

DNA sequences upstream and downstream of a gene which control the rate of transcription.

Question 10

Gene-specific transcription factors

Answer 10

Gene-regulatory proteins which recognise and bind to enhancer sites, acting together to activate or repress gene expression.

Question 11

DNA organisation

Answer 11

DNA is associated with octamers of 8 histone proteins, forming nucleosomes. Nucleosomes coil and condense to form a 30nm fibre of chromatin, which can condense further to form chromosomes.

Question 12

Alleles

Answer 12

Different versions of the same gene, found on homologous chromosomes.

Question 13

Chromosomes

Answer 13

Molecules of DNA, each containing 100s of genes. Every cell has 22 pairs of autosomes and 2 sex chromosomes, comprising one maternal and one paternal copy of the 23 chromosomes.

Question 14

Histone proteins

Answer 14

An octamer is comprised of two H2A, two H2B, two H3 and two H4 histone proteins. They have tails of amino acids which are subject to chemical modifications (eg. acetylation, methylation, phosphorylation) that can act as regulatory information.

Question 15

Histone modification

Answer 15

Enzyme families modify histone tails depending on environmental factors such as cell metabolism and enzyme inhibitors (eg. diet, drugs). This creates a ‘histone code’; a layer of information overlaying the DNA which is involved in regulating gene expression.

Question 16

X-inactivation

Answer 16

A random process occuring in the inner cell mass of the blastocyst, in which one of two X chromosomes is inactivated during early development. The inactive state is passed on to successive cell generations, so is an example of a heritable epigenetic state.

Question 17

Dosage compensation

Answer 17

Females have 2 X chromosomes, whereas males have 1 X and 1 small, gene- poor Y chromosome. X-inactivation equalises gene expression levels between males and females.