1 - Intro To DNA Flashcards

1
Q

What is the structure of DNA?

A
  • Right handed double helix
  • Antiparallel complementary strands held together by hydrogen bonds between complementary base pairs
  • 2-deoxyribose
  • Phosphodiester backbone
  • Polar due to 5’ 3’ ends
  • Major/minor groove
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2
Q

What is chromatin?

A

DNA wrapped around histones (octomer of proteins) , which can then condense to form chromosomes

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3
Q

What is the structure of euchromatin and heterochromatin?

A

Euchromatin: Light. Beads on a string, when DNA being replicated. Less dense as acetylated.

Heterochromatin: Dark, solenoids packed to form a 30nm fibre. Dense as methylated. Gene not expressed like this

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4
Q

What is the name of DNA and a histone together?

A
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5
Q

Where do proteins for DNA replication bind to DNA?

A

Major groove as easily accessible

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6
Q

What is the process of forming a chromosome?

A
  • DNA wraps around histones to form nucleosomes and beads on a string
  • Nucleosomes wrap around one another and form solenoids
  • Solenoids join together to become fibres
  • Fibres zigzag over one another to become highly condensed loops
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7
Q

What is the genome?

A
  • Entired DNA sequence
  • 24 chromosomes, 2 sex 22 auto
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8
Q

What are nucleosides?

A
  • Sugar and base, no phosphate
  • Adenosine, Guanosine, Uridine, Deoxythymidine, Cytidine
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9
Q

What are the two classifications of nucleotide bases?

A
  • Purines (2 C ring): A,G
  • Pyrimidines (1 C ring): T,C,U
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10
Q

How would you find a gene on a chromosome if you knew the exact position?

A

LOOK AT THE BANDING PATTERNS

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11
Q

Why can C only bind to G?

A
  • 3 hydrogen bonds
  • All bonds of nearly equal distance
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12
Q

Why is DNA antiparallel?

A

Ensure the bases are close together and in the middle so they can form hydrogen bonds

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13
Q

What is the nomenclature of DNA?

A
  • Left to right 5’ to 3’
  • Complementary is 3’ to 5’
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14
Q

What is the cell cycle and where are the checkpoints?

A
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15
Q

What is the equation for DNA replication?

A

(dNMP)n + dNTP –> PPi + (dNMP)n+1

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16
Q

What does DNA polymerase do?

A
  • Reads in 3’ to 5’ direction
  • Elongates in 5’ to 3’ direction
  • Catalyses phosphodiester bond using energy from PPi hydrolysis
  • Can proof read
17
Q

How is DNA replication started?

A
  • Primase (RNA Polymerase) makes a primer which binds to the start of DNA wanting to be replicated
  • DNA polymerase binds to primer to start elongation
18
Q

What is the process of DNA replication?

A

1. Initiation

  • Topoisomerase and DNA helicase unwind the double helix to form replication forks with two template strands (one leading one lagging)
  • Primase produces short primers that bind to the 3’ ends of the DNA

2. Elongation

  • DNA polymerase binds to primers and reads in 3’ to 5’ direction, adding complementary base pairs to the primer in a 5’ to 3’ direction
  • On the lagging strand (5’ TO 3’ orientation) there are lots of primers so okazaki fragments are formed and replication is discontinuous

3. Termination

  • Replication forks meet
  • Primers removed and replaced with appropriate bases
  • DNA strand proofread
  • DNA ligase joins okazaki fragments
  • Semi conservative replication
19
Q

If DNA polymerase works at 100 nucleotides a second, and a DNA molecule is 6000 nucleotides long, how long will replication take?

A
  • Impossible to know as there are so many replication forks running in different directions, not just one DNA polymerase
20
Q

How do prokaryotes and eukaryotes differ?

A

Prokaryotes have:

  • Smaller ribosomes
  • Nucleoid (no nucleus)
  • Plasmid
  • Slime capsule
  • Flagella
  • Cell wall of muerin
  • No membrane bound organelles
21
Q

Why are nucleosides used for analogue drugs instead of nucleotides?

A

Nucleotides are charged so would be difficult to get them to cross the membrane