Replication Flashcards
1
Q
DNA
RNA
A
Deoxyribonucleic acid (H at C2) Ribonucleic acid (OH at C2)
2
Q
Monomers of nucleic acids
A
Nucleotides, linked by phosphodiester bonds
3
Q
Nucleotides
A
- 5-carbon sugar → pentose → ribose/deoxyribose
- Nitrogenous base → purine/pyrimidine
- Phosphate group → attached to C5 → -ve charge
4
Q
Nucleoside
A
- 5-carbon sugar
2. Nitrogenous base
5
Q
Purine
A
- 2 rings
- Adenine (A) and guanine (G)
6
Q
Pyrimidine
A
- 1 ring
- Thymine (T)/uracil (U) and cytosine
7
Q
Structure of DNA
A
Pentose sugar + nitrogenous base
→ nucleoside + phosphoric acid
→ nucleotides → (Deoxy)nucleoside[no. of phosphates]
→ nucleic acid (2nm, -ve) + Histones (+ve), electrostatic interactions
→ nucleosomes (euchromatin, 10nm fibre) + linker
→ chromatin fibre/solenoid (heterochromatin, 30nm) + protein scaffold
→ looped domains (300nm)
→ chromatid (700nm)
→ replicated chromosome (1400nm/1.4μm)
8
Q
Nucleic acid
A
- Deoxyribonucleotide is basic unit
- Width btwn 2 sugar phosphate backbones is constant (2.0nm) → combined width of purine and pyrimidine
- 1 complete turn → 10 base pairs → 3.4 nm
- Double helix → antiparallel → right-handed
- Held by weak H bonds btwn nitrogenous bases of opposite strands
- A=T, G≡C → complementary base pairing
9
Q
Structure of RNA
A
- Ribonucleotide is basic unit
- Uracil instead of thymine
- Single stranded (except in some viruses)
10
Q
DNA Replication
A
- Semi-conservative
- Many enzymes and proteins
- Rapid
- Accurate
- S-phase of interphase
- Requires free deoxyribonucleoside triphosphate (dNTP)
11
Q
Semi-conservative
A
- Both parental strands of DNA separate through breakage of H bonds and each act as a template for the synthesis of a new strand through complementary base pairing
- Each DNA molecule formed is a hybrid → 1 original strand, 1 newly synthesised strand
12
Q
DNA Replication steps (4)
A
- Before replication/overview
- Unzipping of parental strands
- Addition of primer
- Synthesis of daughter strands
13
Q
- Before replication/overview (4)
A
- DNA replication occurs at the S phase of interphase
- It is semi-conservative where the original strands of double helix separates and act as templates for synthesis of two new strands
- This gives rise to two new DNA molecules, each consisting of one original and one newly synthesised strand
- Before replication, free activated deoxyribonucleoside triphosphates (dNTP) are manufactured in the cytoplasm and transported into the nucleoplasm via nuclear pores
14
Q
- Unzipping of parental strands (4)
A
- Replication of DNA begins at origin of replication,
- where helicase will bind and unzip and separate the DNA molecule by breaking hydrogen bonds between complementary base pairs
- Single-strand binding proteins keep the strands apart so that they can serve as templates for the synthesis of new strands
- Topoisomerase relieves overwinding strain ahead of replication forks by breaking, swivelling and rejoining DNA strands
15
Q
- Addition of primer (3)
A
- Enzyme primase catalyses the synthesis of a short RNA primer
- which provides a free 3’ OH end for DNA polymerase to recognise and start DNA synthesis of the complementary daughter strand
- as it can only add deoxyribonucleotides to a pre-existing free 3’ OH end of a nucleotide
16
Q
- Synthesis of daughter strands (Basic mechanism) (5)
A
- dNTPs are added to the newly synthesised strand via complementary base pairing with the template strand
- Whereby A forms 2 H bonds with T and G forms 3 H bonds with C
- DNA polymerase catalyses the formation of phosphodiester bonds between adjacent daughter DNA
nucleotides of the newly synthesised strand - Removal of the pyrophosphate (PPi) from the dNTP and the subsequent hydrolysis of PPi provides the energy to drive the polymerisation reaction
- As DNA polymerase moves along the template, it proof reads the previous region for proper base pairing. Any incorrect deoxyribonucleotide is removed and replaced by the correct one
17
Q
- Synthesis of daughter strands (Leading vs lagging strand) (5)
A
- The leading strand is synthesised continuously in the 5’ to 3’ direction
- The lagging strand is synthesised discontinuously, giving rise to Okazaki fragments. Each fragment is initiated by an RNA primer before the addition of DNA nucleotides
- A different DNA polymerase then removes the RNA primer and replaces it with DNA
- DNA ligase seals the nicks by catalysing the formation phosphodiester bonds between Okazaki fragments
- At the end of replication, the complementary parental and newly synthesised DNA strands form a double helix
18
Q
Role of DNA (4)
A
- Main role → store information and pass it on from one generation to the next
- It is a suitable store of information as:
- Can be replicated accurately
- Stable molecule
- Backup of the code
- Coded information readily utilised/accessed
19
Q
- Can be replicated accurately → cbp
A
- Daughter cells have identical copies of DNA as the parent cell
- Weak H bonding between the 2 strands allow them to separate and act as a template for new strand synthesis
- A forms 2 H bonds with T and C forms 3 H bonds with G through complementary base pairing
20
Q
- Stable molecule → bonds
A
- Can be passed on to next generation without loss of the coded information
- Collectively, numerous H bonds hold the two strands of DNA together
- Adjacent nucleotides in each strand joined by strong covalent phosphodiester bonds
21
Q
- Backup of the code → repair template
A
- DNA is double stranded
- 1 strand to serve as a template for the repair of the other if a mutation occurs spontaneously on either one
22
Q
- Coded information readily utilised/accessed → transcription, cbp
A
- Weak H bonding allows the template strand to separate from the non-template strand allowing transcription to take place
- Complementary base pairing allows faithful transfer of info from DNA to RNA in transcription, which will subsequently be translated to protein
23
Q
Telomeres
A
- Nucleotide sequences found at both ends of eukaryotic chromosomes
- Non-coding regions of DNA made up of tandem repeat sequences
- Single-stranded region → 3’ overhang
- Ensure genes are not lost/eroded with each round of DNA replication due to end replication problem
- Prevent loss of vital genetic info with each replication cycle
24
Q
End replication problem
A
- DNA polymerase is unable to replace RNA primers with DNA
- RNA primer removed without replacement → 3’ overhang
- Each round of DNA replication results in shortening of daughter molecules at the telomeres
- Critical length → apoptosis
- Telomerase extends telomeres
