7.1 DNA and DNA replication

Question 1

Draw and label the structure of a nucleosome

Answer 1

see notion

8 histone Proteins form an octomer core. DNA wraps around it twice. Linker DNA connect to the next nucleosome. 9th histone called the H1 protein holds the DNA and histones together

Question 2

describe DNA replication

Answer 2

In Nucleus, occurs in 3’ to 5’ direction

1. gyrase unwinds the DNA
2. helicase seperates the two DNA strands by breaking the hydrogen bonds between the complemtary base pairs
3. single stranded binidng proteins keep the two parent DNA strands seperated
4. DNA primase lays down an RNA Primer (A primer is a short strand of RNA (around 10 bases) that acts as a starting point for DNA replication. It is needed because DNA polymerase 3 can only add nucleotides to an existing strand.)
5. DNA polymerase 3 then adds free nucleotides using complimentary base pairs starting from the the RNA primer (in a 5’ to 3’ direction as it is the opposite strand)
6. on leading strand DNA polymerase 3 can work continously in a 5’ to 3’ direction.
   on lagging strand DNA polymerase 3 cannot work in a 5’-3’ direction continusly and so DNA polymerase 3 has to work backwards in short segments known as Okazaki fragments.
7. DNA polymerase 1 replaces the RNA primer with DNA
8. on lagging strand DNA ligase covalently bonds the sugar phosphate backbone between okazaki fragements together

Question 3

Define coding sequences and repetitive sequences of DNA

Answer 3

coding: exons
non coding: introns
repetitive sequences: sequences that repeat in tandem or are interspersed throughout the genome

Question 4

Outline five functions of non-coding DNA sequences found in genomes

Answer 4

Satellite DNA: tandemly repeating sequences of DNA, used for DNA profiling.

Telomeres: regions of repetitive DNA at the end of a chromosome. Protects against chromosomal deteriorate during replication

Introns: non-coding sequences within genes. Are removed by RNA splicing prior to the formation of mRNA

Gene regulatory sequences: sequences that are involved int the process of transcription includes promoters, enhancers.

Question 5

Outline deduction about DNA structure made from X-ray diffraction pattern

Answer 5

• an x shape is the pattern of a helix
• the regular spacing indicates that the diameter of the helix is consistent

Question 6

Define VNTR

Answer 6

A variable number tandem repeat is sequences of DNA nucleotides that repeat

Question 7

Explain why VNTR are used in DNA profiling

Answer 7

If a region of DNA is cut with a restriction enzyme, the size of the resulting DNA fragments will vary between individuals because different people will have a different VNTRs.

The different fragments will move different distances in a gel electrophoresis allowing us to differentiate between individuals DNA profiles.

Question 8

Explain the Procedure of the Hershey and chase experiment

Answer 8

H.C used a bacteriophage for their experiments. The phage infects bacteria by attaching and injecting genetic material.

H.C labeled the phage protein with radioactive sulfur
Then used a blender to separate the phage from the bacteria
Followed by a centrifuge to separate the phage particles from bacteria
In another experiment H.C labeled the phage nucleic acid with radioactive phosphorus.

Again used a blender and followed by centrifuge

Question 9

Explain how the results of the Hershey and Chase experiment supported the notion of nucleic acids as the genetic material

Answer 9

Because the radioactive DNA from the phage ended up in the bacteria it indicates that it’s the phage DNA that is used to code for the formation of the next generation of phage. The phage proteins were merely packaging used to deliver the dna to the bacterial cell.

Question 10

Outline the mechanism of DNA-histone association

Answer 10

Histones are proteins that have many positively changes amino acids. The positive charge allows them to associate with the negatively charged DNA. Once the charge is neutralized the nucleosomes can tightly pack together.