7.2 Transcription and Gene Expression

Question 1

Promoters

Answer 1

a promoter is a sequence of DNA that is located near a gene
it is the binding site of RNA polymerase
it is not transcribed but is an example of a non-coding DNA having a function

Question 2

How do nucleosomes regulate transcription in Eukaryotes

Answer 2

DNA is wrapped around histone proteins forming nucleosomes
the ends of the histone proteins can be modified
when histone proteins are methylated the transcription of genes can be promoted or inhibited

Question 3

How and why do eukaryotic cells modify mRNA?

Answer 3

the presence of a nuclear membrane means that transcription and translation occurs in different locations
mRNA can be extensively modified before it leaves the nucleus
e.g. introns can be removed from mRNA before translation occurs

Question 4

What is splicing?

Answer 4

splicing of mRNA increases the number of different proteins an organism can produce
some genes code for multiple proteins
these genes have a number of introns that can be spliced out
different variations of the introns that can be spliced out result in a number of different proteins being formed

Question 5

How is gene expression regulated?

Answer 5

it is regulated by proteins that bind to specific base sequences in DNA

Question 6

The Operon Theory

Answer 6

controlling gene expression in prokaryotes
worked out using e.coli (Lac Operon Theory)
why enzyme galactosidase which breaks down lactose, is produced only when lactose is present
one section of DNA that codes for the enzyme is called the structural gene
situated close the another section called the operator gene (activates structural gene when needed)
the operator gene is controlled by the regulator gene, further down DNA chain, this produces a repressor substance which turns the operator gene off (gene repression)
when the enzyme is needed, the repressor substance is inhibited, therefore the operator gene can now turn on the structural gene and the enzyme is made (gene induction)

Question 7

Epigenetics definition

Answer 7

is the study of environmental factors that can turn genes on and off and affect how cells read genes
(the environment of a cell and of an organism has an affect on gene expression)
inheritable

Question 8

DNA Methylation

Answer 8

is a process by which methyl groups are added to the bases cytosine and adenine in DNA
methylation modifies the function of the DNA, typically acting to suppress gene transcription

Question 9

Histone Modification

Answer 9

DNA is wrapped around histones so alterations in the histone can affect the activity of the DNA
methylation of histones can promote or inhibit transcription