transcription and translation - creating proteins

Question 1

what is RNA?

Answer 1

• single stranded (usually)
• sugar is ribose
• has pyrimidine uracil not thymine
• has several forms:
  > mRNA
  > rRNA
  >tRNA
  >siRNA

Question 2

what is mRNA?

Answer 2

>messenger RNA 
>single stranded
> linear, occasionally with hairpins
> intermediate between DNA and protein
> is a copy of DNA which encodes for a specific amino acid sequence

Question 3

What is tRNA

Answer 3

> Transfer RNA
short, RNA molecules
carriers amino acids to ribosomes
the anticodon recognises the sequence of base pairs in the mRNA molecule, which an amino acid is attached at the 3’ end

Question 4

What is rRNA?

Answer 4

> Ribosomal RNA
long molecules in the ribosome with alternating stem and loop structures.
form part of the ribosome
facilitates interaction between mRNA and tRNA
results in translation of mRNA into protein

Question 5

Describe the steps in transcription

Answer 5

> initiation:
- interaction of RNA poly with a specific site on the DNA
- promoter region
- enhancer/silencer region
- requires transcription factors be bound to the promoter region, forming a transcription initiation complex
- this need for transcription factors and enhancers tightly regulates the production of proteins in the cell for use in the body.
transcription:
- RNA pol once initiated, adds complementary RNA nucleotides to create a primary RNA molecule

> splicing:

• once the primary molecule is created, splicing occurs to remove intron (non-coding for protein) regions of the gene
• alternative splicing can create several different proteins

Question 6

Describe translation:

Answer 6

1) mRNA passes through nuclear membrane to ribosomes in cytoplasm or rER
> the anticondon on tRNA recognises and interacts with the codon on mRNA, and the ribosome joins its corresponding amino acid into sequence

Question 7

describe transcription factors

Answer 7

> required for effective transcription
general transcription factors: required for all structural genes
- bind promoter, recruit RNA pol (promoters and enhancers
- required for basal levels of transcription
specific transcription factors: more specialised, activate certain genes for certain stages of development - response to environment
regulatory transcription factors:
- activators and repressors
- regulate rate of transcription of target genes
bind to specific sequences pf DNA in the regulatory regions of their target genes
every transcription factor has a characteristic binding site

Question 8

what are siRNA and micro RNA?

Answer 8

> siRNA - small interfering RNA
- mediate RNA degradation to stop translation
- broad therapeutic application - stop cancer proliferation
- are produced as ds RNA, then cleaved by dicer-mediated cleavage
- ds inactive siRNA binds to RISC (RNA induced silencing complex) and is converted to ss RNA and together with the complex binds with target mRNA and cleavages the mRNA causing degradation.
micro RNA:
- prevents translation of RNA by binding to mRNA and blocking translation
- helps in regulation as mRNA can be quickly activated/deactivated

Question 9

What is epigenetics?

Answer 9

> alters the shape of DNA, not the code itself
creates genetic tags on the DNA (methyl groups), causing the DNA to be tightly wound around histones - methyation
reduces capacity for these genes to be transcribed.
this is how stem cells work in that every stem cell has the ability to become any type of body cell, it only doesn’t due to methylation.
these epigenetic markers can be influenced by the environment and passed onto children