D2.2- Gene expression

Question 1

Gene expression

Answer 1

The mechanism by which genetic information in a gene has an effect on the phenotype produced by transcription, translation and the function of a protein product

Question 2

The regulation of transcription

Answer 2

Transcription is regulated by promoter regions, enhancers and transcription factors

Promoter regions= the location near the beginning of a gene which serves as a binding site for rNA polymerase

Enhancers= a region of DNA located away from the gene (upstream)which allows for an activator protein to attach to it and encourage transcription

Transcription factors=proteins which bind to enhancer regions and interacts and activates promoter regions

This allows a cell to regulate gene translation and select which genes will be transcribed

Question 3

Control of degradation of mRNA for regulating translation

Answer 3

mRNA can be regulated by breaking it up using nuclease enzyme which breaks it into rNA nucleotides which can be recycled.

mRNA may be present from minutes up to days before being broken down.

Question 4

Epigenesis

Answer 4

Process in which a multi cellular organism develops from a zygote through sequences of steps in which cells differentiate and organs form. This is the result from genes plus environment.

Question 5

Epigenetics

Answer 5

The influence of non genetic factors on the expression of genes. That is the modifications of gene expression by epigenetic tags. The phenotype is changed, the genetype isnt.

Question 6

Epigenetic tags

Answer 6

Chemical markers that attach to DNA or histone proteins influencing gene expression. An example is a methyl group is added to DNA nucleotide like cytosine (DNA methylation)

Question 7

Genome, transcriptome and proteome

Answer 7

Genome= all the genetic information of an organism includes coding and non coding sequences

Transcriptome= all the rNA molecules transcribed at a specific time within a cell or organism

Proteome= the compete set of proteins present in a cell or organism at a given time.

Question 8

Why the proteome is larger than the genome

Answer 8

-Alternate splicing of mRNA exons produces multiple proteins.

-Modifications of proteins after translation increases the proteome.

Question 9

Methylation of promotor regions and histones in nucleosomes as examples of epigenetic tags

Answer 9

1. Methylation of promotor regions; methyl group attaches to cytocene nucleotide in a promoter region and represses the activity of the promoter preventing the gene from being transcribed.
2. Methylation of histone in nucleosome; methyl group can also attach to amino acids of histone proteins found in nucleosomes causing transcription to be repressed as DNA binds tighter/unwinds from nucleosome.

Question 10

Epigenetic inheritance through heritable changes to gene expression

Answer 10

Epigenetic changes are inherited by epigenetic tags which dont change DNA sequences.

In mitosis epigenetic tags are passed to daughter cells for the same function.

In meiosis epigenetic tags area erased at fertilisation

Question 11

Epigenome

Answer 11

All the epigenetic tags on DNA and histone proteins

Question 12

Environmental effects on gene expression

Answer 12

Diet, cigarette smoke.

Air pollution; diesel fumes, nitrous oxides, hydrocarbons can add/remove methyl epigenetic tags from a persons epigenome which changes which genes are expressed.

Question 13

Consequences of removal of most but not all epigenetic tags from gamets

Answer 13

Most epigenetic tags are removed at fertilisation in a process called reprogramming which allows the epigenome of the gamete to be specialised producing stem cells.

Some epigenetic tags are not erased.

An example is the phenotypic difference (size/appearance) of tigons and ligers due to imprinted genes.

Imprinted genes is the process in which only 1 of the 2 inherited genes for a trait is expressed. 1 copy of the gene is silenced by epigenetic tags during egg/sperm formation.

Genes from father effecting growth is switched on in ligers. The lion sperm (imprinted to promote growth) was combined with the tiger egg

Question 14

Monozygotic twin studies

Answer 14

MZ twins have the same genome and similar epigenome as they develop in the same uterus. Throughout their life their epigenome becomes increasingly different resulting in different gene expressions. This is used to investigate the effect of the environment on gene expression.

Question 15

External factors affecting gene pattern (1 hormone 1 bacteria)

Answer 15

1. Lactase production in e-coli; e-coli regulates the production of enzymes involved in lactose metabolism. The molecule lac operon regulates the transcription of enzymes required for lactose metabolism. It consists of a promoter, operator, and sequence of 3 genes.

A repressor protein may mind to the operator in the absence of lactose blocking rNA polymerase from transcribing the genes. When lactose is present it binds to repressor proteins to change shape and release from the operator.

Testosterone in regulating gene expression; testosterone diffuses through the plasma membrane of the cell where it binds to the testosterone receptor forming a hormone receptor complex. This moves to the nucleus where it interacts with specific DNA sequences known as androgen responses elements present in the regulatory sections of the target genes. This complex enhances/represses transcription of target genes.