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DNA Structure And Replication Flashcards

1
Q

What is DNA also known as?

A

Chromatin and there are two types

  • Euchromatin: lighter stain
  • heterochromatin: darker stain.

Pg 5

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2
Q

What is the central dogma and where are genes and proteins found?

A

DNA (codes for) RNA (codes for) protein

  • Genes are found in the nucleus
  • Proteins are found in cytoplasm
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3
Q

How do we fit 2M of DNA into 6um cell nucleus?

A

DNA packaging

  • DNA double helix width us 2nm but the total length is 2M

Pg 13-14

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4
Q

What is the first level of DNA packaging?

A

DNA loops around a histone core and this is known as a nucleosome

  • A nucleosome is a histone core with two bits of DNA wrapped around it.
  • made of a histone octamer (8 histone proteins)

Pg 15-16

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5
Q

What is the second level of packaging?

A

Solenoid, this the beads on a string (nucleosomes) tightly packed together.

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6
Q

What makes the heterochromatin and the euchromatin?

A
  1. Heterochromatin:
    - solenoid
    - tightly packed.
    - genes are not encoded
  2. Euchromatin
    - Beads on a string
    - not tightly packed
    - gene expressed
  • The genes are expressed on the Euchromatin because the DNA is more accessible than in the solenoid.

Pg18

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7
Q

What is the structure of a chromosome?

A
  • A chromosome, is lots of solenoid loops tightly packaged in different levels of packaging of solenoid loops.
  • If you keep unwinding the solenoid loop, you get the beads on the string, then the nucleosome, then the DNA, the the gene.
  • Genes are stretches on DNA. On the double helix

Pg 21-24

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8
Q

What do genes do and where are they found?

A

Genes carry the code for proteins.

Genes have a chromosomal location.

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9
Q

What is a genome?

A

The entire DNA sequence of a protein.

Human genome is 24 chromosome (23 for male and female)

  • 22 autosomal plus 2 sex chromosomes X and Y
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10
Q

What is the difference between RNA and DNA pentose sugar?

A
  • carbon 3 on the ribose sugar has a hydroxyl group, whereas carbon 2 on the deoxyribose had just hydrogen
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11
Q

What are the two nitrogenous bases?

A

Purine (Guanine and Adenine - 2 ring structure

Pyrimidines (Cytosine, Thymine and uracil) - 1 ring structure

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12
Q

What is a nucleotide and what is a nucleotide?

A

Nucleoside - (pentose)sugar and nitrogenous base

Nucleotide - (pentose)sugar, (nitrogenous) base and phosphate

  • Nucleosides can be phosphorylated to form nucleotides.
  • Nucleotides can have one or more phosphates.

Pg 42-44

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13
Q

What bind joins nucleotides together and what is a feature of the chain?

A

Phosphodiester binds

  • chain polarity
  • chain has distinct ends: 5’ P end and 3’ OH end.
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14
Q

What is the secondary structure?

A

The bond formed between the bases

  • there are areas of electro negativity and positivity that attract to each other
  • guanine and cytosine form 3 hydrogen bonds between each other
  • adenine and uracil or thymine form 2 hydrogen bonds

Pg 47-55

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15
Q

What is the structure of DNA? (secondary structure)

A
  • Duplex structure
  • It is complementary and anti parallel
  • Each single strand is held together by covalent binds between sugar-phosphates
  • The double strand is helped together by hydrogen bonds between complementary base pairs.

Pg 58-60

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16
Q

How is the strand written?

A

5’ to 3’
3’ to 5’

Pg 61-65

17
Q

What do each strand of DNA act as and what is DNA replication needed for?

A
  • Each DNA strand acts as a template for a new strand.

- DNA replication is important for the process of cell division

18
Q

Where does DNA replication take place in?

A
  • S phase of the cell cycle

- S phase is when DNA synthesis takes place, this is where all the DNA is replicated.

19
Q

What type of process is DNA replication?

A

It is a semi-consevative process.

  • Where the old DNA stand acts a template for the new DNA strand
  • After DNA replication each DNA molecule contains a old stand and a new strand.
20
Q

What strand is read and what strand is made in DNA replication?

A
  • The strand that is read, is read 3’ to 5’.
  • The strand that’s made, is made 5’ to 3’
  • Phosphodiester bond is created
  • Pyrophosphate is released (PPi)

Pg 72

21
Q

What is the formula for DNA replication?

A

(DNA)n + dNTP - (DNA)n+1 + PPi

N is the base

Pg 73

22
Q

What are the features of DNA replication?

A
  • Catalysed by DNA polymerase (responsible for DNA synthesis)
  • Hydrolysis of PPi by pyrophosphatase drives the reaction (from left to right)
  • dNTPs needed (base)
  • Separation of the double stranded DNA template
  • Stepwise faction
  • Synthesis from 5’ to 3’
23
Q

What type of chromosomes do prokaryotes have and what are the different steps of DNA replication?

A
  • Circular naked DNA
  1. Initiation
  2. Elongation
  3. Termination
24
Q

What main things that occur in initiation process in DNA replication for prokaryotes?

A
  1. In initiation there is a circular double stranded DNA molecule, at a certain position the two strands will separate.The two separated strands can be used as templates.
  2. The part where it separates is known as the Origin of Replication.
  3. There are two replication forks moving in either direction from the origin of replication.

Pg 75

25
What are the main things that occur in the elongation step of DNA replication in Prokaryotes?
- Replication continues as the replication forms are moving in opposite directions. Pg 75
26
What are the main things that occur in the termination step of DNA replication in Prokaryotes?
* When the replication forks finally meet each other, that’s when you get termination. * Then you have two circular double stranded DNA molecules that are identical copies of each other.
27
What occurs in initiation step of DNA replication in eukaryotes?
* Recognition of origin of replication * Requires recruitment of DNA polymerase (+ other proteins) • Requires a ‘kick-start’ by DNA primase (making a short RNA primer) as DNA polymerase can only extend a 3’end. • One origin of replication results in two replication forks. Pg 77-80
28
What does DNA primase do?
- Needed to kick start replication as it makes a short piece of RNA and the the DNA polymerase finishes it off. - Both the leading (3 to 5 strand and the lagging strand (5 to 3) need primase. - But the lagging strand needs a new primer each time the DNA is unzipped, whilst the leading strand only needs it once. Pg 82
29
What occurs in elongation step of DNA replication in Eukaryotes?
1. DNA polymerase is extended and making newly synthesised strand 2. DNA Helicase unwinds and unzips the DNA double helix. 3. The leading strand is made continuously as it is because the template strand is in the correct direction of replication for DNA polymerase( 3 to 5 and synthesised 5 to 3 ) - The lagging strand is made discontinuously in fragments (okazaki fragments because it is the wrong direction for DNA polymerase (only reads 3 to 5 and synthesis 5 to 3). 4. DNA ligand fuses the gaps of the Okazaki fragments of the lagging strand. Pg 83-91
30
What occurs in termination step of DNA replication in eukaryotes?
The two replication forks meet 2. DNA ligaments joins final fragments Together 3. Resulting in two identical DNA molecules (semi-conservative). Pg 92-95
31
What occurs in DNA replication in eukaryotes?
- Eukaryote DNA isn’t circular chromosome but linear chromosome. - Before replication : one chromosome =one DNA molecule - There are many origins of replication, sequences where replication starts, loads of replication forks meet each other. - After replication: one chromosome = two DNA molecules. Pg 96
32
What is a replicated chromosome?
- A replicated chromosome consist of 2 chromatids, held together by a centromere - Centromere is a protein molecule holding two DNA molecules together after replication. Pg 97

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