DNA REPLICATION

Question 1

How is DNA arranged in eukaryotic cells

Answer 1

Most in the nucelus
A chromosome is DNA coiled around proteins called hustones
Each chromosome is one molecule fo DNA

There’s also loops of DNA without hit one protiens inside mitochondria and chloroplasts

Question 2

Prokaryotes - how is DNA organised

Answer 2

In a loop in the cytoplasm, not enclosed in a nucelus and not wound around his tone proteins

Question 3

Brief outline of DNA replication

Answer 3

For DNA to replicate, the double helix has to unwind and separate into 2 strands, so TEH hydrogen bonds holding bases together have to be broken
Free DNA nucleotides will pair with complementary bases, which have been exposed
H bonds between them
New nucleotides join to adjacent nucleotides with phosphodiesterbonds

Question 4

Why is DNA replication semi conservation

Answer 4

Each strand chains one old and one new strands

Question 5

What does gyrase do

Answer 5

Untwists the double helix

Question 6

What does helicase do

Answer 6

Breaks the hydrogen bonds between nitrogenous bases, unzipping the DNA

Question 7

What does DNA polymerase do

Answer 7

New phosphodiesterbonds bonds along the backbone, travels only form the 5’ to 3’ direction

Question 8

What does ligase do

Answer 8

Seals the sugar phosphate backbone to join together the lagging strand

Question 9

Name the enzymes involved in DNA replication

Answer 9

Gyrase
Helicase
DNA polymerase
Ligase

Question 10

What happens in DNA replication

Answer 10

1. Double helix unwinds and unzips as the hydrogen bonds between bases are broken
2. This leaves neucelotide bases exposed
3. Free nucleotides move towards exposed bases of DNA unwound strands. They are activated with 2 extra phosphates( ATP)
4. The polynetuclotide chains act as templates for the assembly of neucelotides
5. Complementary base pairing occurs between exposed bases and free activated nucleotides- h bonds
   Polymerase seals the back bone

Question 11

Lagging strand - DNA polymerase

Answer 11

The lagging strand is from the 3’ to 5’ direction

DNA unzips in one direction

Synthesised dis continuously

OKZAZKI fragments are later catalysed and joined by ligase enzyme

Question 12

Leading strand - DNA polymerase

Answer 12

Runs from 5’ to 3’ strand

Synthesised continuously

Question 13

What errors could occur during replication

Answer 13

Sequence of bases may not be matched

Incorrect sequence may occur in newly copies strand - wrong neucelotide may be inserted
Random + spontaneous
Could change the genetic code =mutation

Question 14

How are errors minimalists

Answer 14

There are enzymes that can proof read and edit out incorrect neucelotides = reduce mutation rate

Question 15

How often do replication errors occur

Answer 15

1 in every 1*10^8 base pairs

Question 16

What is the genetic code

Answer 16

The sequence of bases in DNA

Determines the sequence of amino acids in the polypeptide

Question 17

What is the triplet code

Answer 17

3 bases code for 1 Amino acid

Each triplet is called a codon

Question 18

What is a gene

Answer 18

Section of DNA that contains the sequence of bases to code for an entire protein

Question 19

Properties of genetic code

Answer 19

Degenerate 
DNA codes for a sequence of amino acids 
Start and stop codons- every polypeptide starts its methyaline
Universal - found in all amino acids
Non overlapping 
Evolved a long time ago

Question 20

How many base triplets are possible

Answer 20

64 different base triplets possible( 444)

Question 21

Why is the genetic code degenerate

Answer 21

20 amino acids that occur in biological proteins regularly
Lots more codons than amino acids

Many amino acids cna be coded for by more than 1 codon

Question 22

Why is the genetic code non overlapping

Answer 22

Read from base 1 rather than base 2 or 3