DNA replication & Cell processes - DNA replication & gene expression

Question 1

What is DNA replication?

Answer 1

The process of making two molecules of DNA from one molecule of DNA

Question 2

What is DNA structure?

Answer 2

Contains Sugar, Phosphate + nitrogenous Base
Backbone is formed by 5’ to 3’ Phosphodiester linkages
Circular DNA may be supercoiled or relaxed which lies freely in cytoplasm

Question 3

How many bonds are formed between bases

Answer 3

Thymine + Adenine = Two hydrogen bonds between bases
Cytosine + guanine = three hydrogen bonds between bases
Purines will always bond to pyrimidines

Question 4

What is Semi conservative replication?

Answer 4

DNA replication occurs as new strand forms from template strand (one old – one new)
Each round of replication, the parent molecule unwinds and two template strands form.

Question 5

Describe the unwinding of DNA

Answer 5

Helicases break hydrogen bonds between base pairs (requires energy from ATP)
Unwinding places strain on other parts of molecule “overwinding”– DNA gyrase prevents supercoiling
Prokaryotes: one replication origin & replication forks move outwards
Eukaryotes: many replication origins

Question 6

What are primers?

Answer 6

Required for DNA replication. They are synthesised by primase & removed at later stage of DNA rep

Question 7

What is the role of DNA polymerase?

Answer 7

Aids in DNA replication, requires a primer for DNA replication to occur
Structure like a ‘right hand’ exonuclease removes incorrect nucleotides

Question 8

Explain DNA replication

Answer 8

DNA replication always occurs 5’ to 3’ (New nucleotides can only add to 3’ carbon as it contains an OH group)
DNA replication occurs in the same direction BUT leading strand =1 direction lagging strand = other direction

Question 9

Explain the role of the replication fork

Answer 9

Single stranded binding proteins which stops single stand being degraded & stops strand from re-joining
Primosome- contains primase ready for lagging strand DNA replication

Question 10

Explain the steps of lagging strand synthesis

Answer 10

Primosome produces primase binds to DNA strand
DNA polymerase III adds nucleotides
DNA polymerase I removes primer + adds nucleotides
DNA ligase joins okazaki fragments

Question 11

What is transcription?

Answer 11

Synthesis of mRNA from DNA template

Question 12

What is translation?

Answer 12

Protein synthesis using mRNA

Question 13

What are the different types of RNA?

Answer 13

mRNA is messenger RNA (comes from DNA)
tRNA carries amino acids, used in translation
rRNA Ribosomal RNA which make up RNA structure of ribosome

Question 14

What are the stages of translation?

Answer 14

Initiation
Elongation
Termination

Question 15

Describe intiation

Answer 15

Promoter regions are found upstream of transcription start site (5’ end) at TTGACA (-35) the region that shows: Where RNA polymerase should join, which strand to use, which direction RNA polymerase should move in
TATAAT box also acts as a promoter region (-10)

Question 16

Describe elongation

Answer 16

DNA strand unwinds 17 base pairs at a time
RNA polymerase forms “a bubble” around DNA strand and moves down the DNA strand
Strand is unwound and at one end and rewound at the other end

Question 17

Describe termination

Answer 17

Occurs in 2 steps, Rho independent & Rho dependent

Question 18

Describe rho independent termination

Answer 18

Transcription may terminate at this hair pin loop to structure transcribed for looks like hair pin followed by many uracil bases so section cleaves off and mRNA strand is terminated

Question 19

Describe rho dependent termination

Answer 19

Rho protein is ATP dependent
Pulls the mRNA away from RNA polymerase + DNA template

mRNA has the same nucleotide sequence as the coding strand, but it contains uracil