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BIOSCI 101 > Lecture 5: Nucleic acids > Flashcards

Lecture 5: Nucleic acids Flashcards

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1
Q

What are the 4 types of nucleic acids in our cells

A

DNA and RNA: involved in informational processes in the cell.

ATP: stores and transports chemical energy within the cell.

cAMP: derived from ATP involved in intracellular signalling

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2
Q

DNA is a polymer of nucleotides. How to nucleotides join together

A

The phosphate group (5’ end of nucleotide) is added to the sugar of the next nucleotide (3’ end) by covalent phosphodiester bonds, generating the sugar-phosphate backbone.

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3
Q

What makes a nucleotide

A

Phosphate group - sugar (pentose) and nitrogenous base

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4
Q

What are differences between the components of nucleotides and ribonucleotides

A

The sugar in DNA is deoxyribose, the suger in RNA is ribose. The Purines (adenine and guanine) and pyrimidine cytosine are the same but DNA uses thymine while RNA uses Uracil.

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5
Q

What is the nucleic acid structure of RNA vs DNA

A

RNA form unique 3D shape, RNA exist as single strands which can H bond with itself nitrogenous bases. This is more variable. DNA has 2 nucleic acids paired H bonding with nitrogenous bases in an alpha helix

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6
Q

Where is the cellular location of DNA

A

In prokaryotes: conc in the nucleoid, eukaryote: in nucleus and found in mitochondria & chloroplasts.

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7
Q

What is the directionality of the DNA and why is adding nucleotides in this direction

A

5’ to 3’ direction. Because 3’ has -OH of sugar- available to bind to a new phosphate and on the 5’, there is a phosphate group allowing phosphodiester bond to form

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8
Q

What does ‘antiparallel’ double helix structure mean

A

the nitrogenous bases are complementary paired by one strand is 5’ to 3’ and the other strand is 3’ to 5’

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9
Q

What forces are between the nitrogenous bases

A

van de waals forces because they are hydrophobic molecules closely stacked together

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10
Q

How is DNA densely packed into a chromosome

A

DNA helix wraps twice around 8 histone proteins forming a ‘nucleosomes’. The tails of the histones radiate out of the nucleosomes.
The tails associated with neighbouring DNA strands and nucleosomes giving rise to a fibre.
Next, a protein scaffold is used for the fibre to loop and anchor to make the looped domains. which bundles into the Chromosome

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11
Q

What is the ribosomal RNA

A

RNA component of ribosome made from nucleolus from repetitive DNA that helps support the structure of the ribosome and involved in protein synthesis.

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12
Q

What is the function of messenger RNA (mRNA)

A

Conveys info about amino acid sequence of peptide from DNA in nucleus to Ribosome in cytosol.

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13
Q

What are the relative amounts of rRNA, mRNA.

A

rRNA is stable and contributes bulk of cellular RNA. mRNA is synthesised at a fast rate and degrades rapidly so only present in relatively small amounts.

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14
Q

What is structure of tRNA

A

it contains 4 base-paired regions with itself and 3 loops, one at the bottom= anticodon. It also has an amino acid attachment site at the top.

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15
Q

What is the function of tRNA

A

Translates nucleotide sequence in mRNA into amino acids during protein synthesis. one specific tRNA for each amino acid.

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16
Q

What is the basic concept of DNA replication

A

The 2 strands of the parent strands are separated and then 2 daughter DNA molecules that are identical to the parent strand. This is by multienzymic complex, accurate and fast.

17
Q

What are the 3 models of DNA replication originally proposed

A
  1. Conservative: 1st replication has 2 parent strand together and 2 new strands together .
  2. Semiconservative: two parental strands separated. 1st replication: one strand parent and one strand new in each
  3. Dispersive: 1st replication has a mix of new and parent in both two strands of the daughter DNAs
18
Q

Compare the origins of DNA replication in prokaryotes vs eurkaryotes

A

Prokaryotes have one origin of replication but Eukaryotes have multiple. All points of origin start replication simultaneously in opposite directions from the point, making a bubble around the point with 2 replication forks on both sides, which eventually join up and separate the 2 DNA molecules.

19
Q

What are 4 the proteins involved in initiation of replication

A
  1. Helicase: unwinds the DNA by breaking the H bonds between nitrogenous bases.
  2. Single strand binding proteins: bind to single strands of DNA to stop them from reassociating with each other. They also stop DNA from bending and kinking.
  3. Topoisomerase: break the sugar backbone, swivels and rejoins the overcoiled region of parent DNA ahead of the fork. Relieve strain caused by DNA unwinding.
  4. Primase: Synthesis short RNA primers (5-10 nucleotides) using the parental DNA as template which makes a 3’ end for DNA polymerase to add the DNA nucleotides to.
20
Q

What provides the energy to drive replication and what enzyme does adding nucleotides involve.

A

It is added to the 3’ end with free OH. DNA polymerase will catalyse the addition. Phosphate bonds to phosphate are hydrolysed and 2 P are broken away leaving only one phosphate to bond. The energy released from this hydrolysis drives replication

21
Q

What model of replication does DNA take

A

semiconservative

22
Q

Why is DNA replication Bi-directional

A

Replication occurs in both directions from the origin of replication on the top strand and bottom strand. The new strand that is synthesised must be antiparallel to the parent template. As DNA can only be synthesised in 3’-5’ direction, there is a leading strand and lagging strand from the point of origin of one parent strand.

23
Q

Describe how the continuous synthesis on the leading strand works

A

The leading strand is synthesised from an RNA primer at bound at the point of origin to make a 3’ ready for the DNA pol III to add nucleotides to the end of the fork, slid along by the sliding clamp.

24
Q

Describe how the discontinuous synthesis on the leading strand works

A
  1. Primase generate RNA primer.
  2. DNA polymerase III adds nucleotides to the primer forming okazaki fragment.
  3. DNA pol II detaches once it reaches the next RNA primer.
  4. Okazaki fragment II is primed, and DNA pol III adds nucleotides, detaching when it reaches the primer for fragment 1.
  5. DNA pol I replaces RNA primers with DNA
  6. DNA ligase forms bonds between DNA fragments.
25
Q

How is accuracy ensured in DNA replication

A

DNA polymerase can proofread and repair DNA as it is made

26
Q

What are Telomeres purpose

A

These are regions of repetitive nucleotide sequences at the end of each chromatid which prevent the loss of genes due to shortening in the replication process.

27
Q

What is the difference between the leading and lagging strands

A

Leading strand is adding nucleotides in the same direction as 3’ to 5’ away from the origin. However Lagging strand is adding nucleotides from the point of origin to the fork where it going in the opposite direction from 5’ to 3’ so it has to add it in fragments, going a bit ahead to prime and then filing the DNA back to the origin the 3’ to 5’ way

28
Q

What enzyme replaces lost telomeric sequences in continuously dividing cells

A

Telomerase

29
Q

What causes a shortening of the ends of DNA molecules each time a cell divides

A

On the lagging strand the final primer on the end can be removed by cannot be replaced by DNA as the end to attach DNA to is only a 5’, therefore after the 1st round of replication lagging strand is shorter than template, and then next round the new leading and lagging strand are shorter than original template

30
Q

What is the difference between Heterochromatin and Euchromatin

A

Heterochromatin is highly condensed, inactive and chromosome- this is methylation of histone tail
Euchromatin is less condensed and active- this is acetylation of histone tail

BIOSCI 101 (23 decks)

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