DNA to proteins

Question 1

DNA vs RNA:

Answer 1

DNA - Double stranded, ATCG, present at all times
RNA - Single stranded, UTCG, tRNA, mRNA, rRNA, only present following cell stimulation.

Question 2

What is a transcription factor?

Answer 2

Protein which binds to promoter region. They find their way to specific sequences on 5’ of exon

Question 3

What is a promoter region?

Answer 3

Binding sites for transcription factors. Has a specific sequence of nucleotides at 5’

Question 4

What is a transcription complex?

Answer 4

When transcription factors bind to promoter region and RNA polymerase joints to form a complex.

Question 5

Briefly state the points of transcription:

Answer 5

1. Topoisomerase + DNA helicase unwinding, SBB coating
2. mRNA nucleotides line up
3. RNA polymerase 2 joins nucleotides
4. mRNA leaves nucleus. attach to ribosome
5. mRNA transcribed using tRNA.
6. Peptide bonds form - protein

Question 6

Explain transcription in detail:

Answer 6

1. Topoisomerase unwinds the double helix by relieving the supercoils. DNA helicase separates DNA. SSB’s coat the DNA to prevent re annealing.
2. Free mRNA nucleotides line up next to complementary bases on the template strand, UT CG.
3. RNA polymerase 2 joins mRNA nucleotides by phosphodiester bonds and forms an antiparallel mRNA strand starting at a promoter region. Transcription stops at stop codon.
4. mRNA leaves the nucleus and attaches to an 80s
   ribosome.
5. At ribosome, mRNA, bases read in threes, sequence is used as a template to bind to complementary tRNA molecules at their anticodon, which have specific amino acids attached. Bases are read 5’ to 3’
6. Enzymes remove amino acid from tRNA, amino acids are joined by peptide bond via condensation reactions. Forms a polypeptide chain - protein.

Question 7

What is the code for start codons?

Answer 7

AUG

Question 8

What is the code for stop codons?

Answer 8

UAG - UGA - UAA

Question 9

Where is mRNA made?

Answer 9

Nucleus

Question 10

How does ribosome recognise mRNA?

Answer 10

Ribosome recognises mRNA from the CAP at the 5’

Question 11

What are the regions of a gene?

Answer 11

Intron - non coding part of gene
Exon - coding part of gene
Promoter region - RNA polymerase recognises and binding site for transcription factors

Question 12

What is a mRNA primary transcript?

Answer 12

When the mRNA strand is completely complimentary to the original copy of the DNA.

Question 13

How does the mRNA strand go from primary to mature?

Answer 13

Introns are removed and exonic regions are joined together.

Question 14

What is exon shuffling, what does it allow?

Answer 14

Exons are not in the same order, allows new proteins to be made e.g the immune system.
Thus exon shuffling enable huge variants of antibodies etc. to be produced

Question 15

What are the feature of the genetic code?

Answer 15

Degenerate - More than one codon for an amino acid
Universal - All organisms use the same code, less than 10 exceptions
Non overlapping - Bases are read in threes, codons. Read once only.

Question 16

What are factors that initiate gene expression and how do they work?

Answer 16

Proteins that are called transcriptional factors, bind to promoter region, form transcriptional complex.
Causes DNA to unwind and strands to separate.

Question 17

What are factors that turn off gene expression and how do they work?

Answer 17

This is the activation of repressors (RNA polymerase binding inhibitors).
Enzymes aren’t activated, transcription can’t take place, RNA polymerase needed.

Question 18

What is silencing a gene and how does it work?

Answer 18

DNA can be chemically altered via methylation.
Eg. Macrophages where immunoglobulins not produced, gene for producing immunoglobulins are silenced, DNA in heterochromatin state.

Question 19

Heterochromatin vs Euchromatin:

Answer 19

Heterochromatin - Tightly wound DNA, gene silenced
Euchromatin - Loosely wound DNA, gene expressed