DNA replication & Cell processes - DNA replication & gene expression Flashcards Preview

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Flashcards in DNA replication & Cell processes - DNA replication & gene expression Deck (19)
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1
Q

What is DNA replication?

A

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

2
Q

What is DNA structure?

A

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

3
Q

How many bonds are formed between bases

A

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

4
Q

What is Semi conservative replication?

A

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.

5
Q

Describe the unwinding of DNA

A

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

6
Q

What are primers?

A

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

7
Q

What is the role of DNA polymerase?

A

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

8
Q

Explain DNA replication

A

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

9
Q

Explain the role of the replication fork

A

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

10
Q

Explain the steps of lagging strand synthesis

A

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

11
Q

What is transcription?

A

Synthesis of mRNA from DNA template

12
Q

What is translation?

A

Protein synthesis using mRNA

13
Q

What are the different types of RNA?

A

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

14
Q

What are the stages of translation?

A

Initiation
Elongation
Termination

15
Q

Describe intiation

A

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)

16
Q

Describe elongation

A

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

17
Q

Describe termination

A

Occurs in 2 steps, Rho independent & Rho dependent

18
Q

Describe rho independent termination

A

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

19
Q

Describe rho dependent termination

A

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