Gene expression and protein biology

Question 1

structure of gene

Answer 1

Gene: the unit of inheritance. Genes encode the information for making proteins.

Genome: sequence of all the DNA in an organism (genes + non-protein coding regions)

Question 2

process of transcription

Answer 2

mRNA catalysed by RNA polymerases
Error rate of one mistake every 104 nucleotides

Initiation

• RNApolymerase II binds the start of a gene
  DNA strands separate
  Elongation

-RNA strand grows – transcription bubble
Termination

-RNApolymerase II dissociates

Question 3

transcription factors

Answer 3

Transcription factors (TFs) are proteins bind to short but VERY specific sequences of DNA (TATA box)

TFs affect rate of transcription (positively or negatively)

Turn genes “on” or “off”
“activators” or “repressors”

Basal TFs promote the binding of RNApolymerase II (general TF complex)

Question 4

clinical significance of transcription factors

Answer 4

Mutation in TATA box
β-globin (HBB) gene promoter mutation
mRNA sequence and protein structure unchanged, amount of mRNA made is reduced
Thalassaemia (severe anaemia)

Mutation to transcription factor
A p53 gene mutation occurs in ~50% of skin cancers
Disrupts the normal cell cycle

Question 5

enhancers and silencers

Answer 5

TFs affect rate of transcription
TF binding results in low basal levels of transcription

Turning gene transcription ‘on’ with TFs can be boosted by TF binding to ‘enhancers’ OR prevented by ‘silencers’

Question 6

activator and repressor transcription factors

Answer 6

TFs are extremely specific

Basal TFs allow for expression of a gene at low, baseline level

Activator TFs increase gene expression and repressor TFs reduce gene expression

Enhancers and silencers are DNA regions that TFs bind to, to enhance or silence gene expression

These can be upstream, downstream, close or very far away in the genetic code

Question 7

closed and open DNA

Answer 7

DNA is not always accessible to TFs
Proteins called histones bind DNA and form larger nucleosomes
Wrapped up closed DNA

Question 8

Constitutive gene expression

Answer 8

Genes which are expressed in all cells, all the time, at about the same level
Housekeeping genes: maintain basic cell function
- have a constitutive promoter

Question 9

inducible gene expression

Answer 9

Genes which are
only expressed in certain tissues or cells
only expressed at certain times

Question 10

locus control regions

Answer 10

-Open chromatin spanning several genes
Example: Globin genes (involved in producing haemoglobin)

Transcription factors bind to globin LCR – only in erythroid progenitors
Opens DNA of all globin genes
Gene expression possible

Question 11

proteolysis

Answer 11

Proteolysis is the cleavage of a protein

Is often used to activate an inactive protein (zymogen)

The clotting cascade involves several serine proteases that become sequentially activated

Pro-thrombin is lysed at a specific serine residue to form thrombin

Question 12

mutations and protein function

Answer 12

Different types of genetic mutation have different effects on protein function

Cystic fibrosis is an autosomal recessive condition

Caused by mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) protein which is a chloride ion channel present in epithelial cell membranes

CFTR normally regulates mucus transport in the lungs and pancreas

Question 13

mutations

Answer 13

Substitution/deletion/insertion of a different amino acid can cause protein conformational change – affecting function

Question 14

pharmaceutical protein-based therapies

Answer 14

Recombinant proteins (enzyme replacement therapy, hormone replacement therapy)
Insulin, growth factor, oestrogen
Antibodies (immunotherapy)
Peptide mimetics
Inhibitors of protein function