Wk4 Storage And Retrieval Of Genetic Information

Question 1

What is the central dogma of molecular biology ?

Answer 1

Passage of genetic information - 1 way process

Question 2

Why is dna stored in eukaryotic nucleus?

Answer 2

Stores sequence for proteins to be expresssed

Question 3

What is the only thing to reverse transcription?

Answer 3

Reverse transcriptase (retrovirus)

Question 4

DNA vs RNA

Answer 4

Both have phosphate backbones
DNA
double-stranded
high molecular weight
Uses T
Stable

RNA
single-stranded - intra-molecular base pairing (RNA can form hydrogen bonds)
heterogeneous in size
Has an OH group at ribose C2 that DNA doesn’t have
Uses U
Unstable

Question 5

DNA summary

Answer 5

• Bases pair because of hydrogen bonding
• There is room for 1 purine + 1 pyrimidine inside the helix
• The base sequence of one strand determines the sequence of the other strand

Question 6

What makes up the genome?

Answer 6

Genes = <5%

• ‘Promoter’ & ‘enhancer’ elements
• 5’ (upstream) and 3’ (downstream) of gene
• Typically several per gene
• Can be ~450kB from gene

Question 7

What is non-coding DNA?

Answer 7

Even genes are broken up by stretches of non-coding DNA
Exons = coding DNA (they are ‘Expressed’)
Introns = non-coding DNA (they are ‘intervening’)
Introns removed from primary RNA by ‘splicing’ machinery

Question 8

What are repeated elements?

Answer 8

Common

Derived from virus

• Most common repeats are LINE & SINE families
• Vary in size
• Represent ~25% of our DNA
• Can be used to detect polymorphisms (‘DNA fingerprinting’)

Question 9

What is DNA replication?

Answer 9

Turning it into 2 copies

Question 10

What is semi-conservative replication?

Answer 10

DNA helix that contains one strand from helix it was copied from

Question 11

What are the building blocks of DNA synthesis?

Answer 11

Deoxynucleoside triphosphates

Question 12

What direction does DNA synthesis occur?

Answer 12

5’ to 3’

Question 13

DNA polymerase

Answer 13

Proceeds in a 5’ to 3’ direction
Adds 1000 bases /second to the chain
Require dNTPs
Must have a template and an RNA primer

Question 14

What does DNA polymerase do?

Answer 14

1. DNA is pulled apart and copies of both stands made
2. Top stand = leading strands
3. DNA polymerase keeps on a 5-3 point direction, copying leading strand continuously
4. Logging strand leaves a gap that must be filled but DNA polymerase cannot go backwards
5. So instead it binds in different points in gaps - making little DNA fragments (Okazaki fragments) to form a continuous DNA strand

Question 15

DNA to RNA transcription

Answer 15

• RNA synthesis needs DNA template
• building blocks: nucleoside triphosphates
• RNA is synthesised in a 5 to 3 direction
• only one strand is copied
• RNA polymerase adds 50 bases per second

Question 16

What is the spliceosome?

Answer 16

The primary RNA transcript binds proteins involved in RNA processing

Local DNA melting produces ~30bp bubble

As the bubble moves along the DNA, the RNA chain extends

Question 17

What are ribosomes?

Answer 17

Complexed that assemble strings of amino acids (proteins) as instructed by the mRNA sequence

Question 18

What is tRNA?

Answer 18

An adaptor molecule

• 3 hairpin stem loop structures
• stabilised by base pairing
• distinctive functional region
• responsible for recognising sequence on mRNA and recognising specific amino acid
• structure reinforced by hydrogen bonds

Question 19

The genetic code

Answer 19

• read in groups of 3 bases
• read in a 5’ to 3’ direction
• 3 possible reading frames
• each amino acid is coded for by a codon
• some amino acids have more than one codon
• some have only one codon
• 3 codons do not encode amino acids