DNA replication

Question 1

How is dna organised in eukaryotes

Answer 1

Most in the nucleus

1 DNA and his tone proteins - 1 chromosome

Each chromosome is 1 molecule of DNA

LOOP of DNA without his tone Protejns inside mitschondria and chloroplasts

Question 2

Prokaryotic cells _ DNA arrangement

Answer 2

In a loop in the cytoplasm , not enclosed in a nucleus

NOT wound around histone proteins

Question 3

What does self conservative replication mean

Answer 3

For DNA to replicate, the double helix has to unwind and separate into 2 strands, so H bonds holding bases together must be broken

Free DNA nucleotides will pair with complementary bases, which has been exposed

H bonds form between them

Nucleotides join to their adjacent nucleotides- with PHOSPHODIESTER bonds

Each strand gets 1 old and 1 new dna strand -

Question 4

Gyrase

Answer 4

Untwists the double helix

Question 5

Helicase

Answer 5

Breaks the H bonds between the nitrogenous bases

UNZIPS the DNA

Question 6

DNA polymerase

Answer 6

New PHOSPHODIESTER bonds along new backbone

Only travels from the 5’ to 3’ direction

Catalysed between neucleotides

Question 7

Ligase

Answer 7

Seals the sugar phosphate backbone to join together the pieces of the lagging strand

Question 8

Why is dna replication semi conservative

Answer 8

Each strand of the new dna molecule contains 1 new and 1 old strand

Question 9

What happens in DNA replication ??

Answer 9

1. The double helix unwinds and unzips as H bonds between bases are broken

2 this leaves neucleotide bases exposed

3. free neucleotides move towards exposed bases of DNA !!!!!!!
4. The poly neucleotide chains act as templates for the assembly of neucleotides
5. Complementary base pairing occurred between free activated neucleotides and exposed bases - h bonds
6. DNA polymerase forms covalent PHOSPHODIESTER bonds between free neucleotides that have attactched to each template
7. 2 daughter DNA molecules form separate double helix

Question 10

DNA polymerase - leading strand

Answer 10

The leading strand runs from 5’ to 3’ end

Synthesised CONTINUOUSLY

Question 11

Lagging strand - DNA polymerase

Answer 11

Leading strand is from 3’ to 5’ direction

DNA unzips in one direction -

Synthesised discontinuously

Get Okazaki fragments that are later catalysed and joined by ligase enzymes

Question 12

What errors could occur during replication ?

Answer 12

Sequence of bases may not be matched correctly

Incorrect sequence may occur in newly copied strand - wrong neucleotide may be inserted

RANDOM and SPONTANEOUS

Could change he generic code - mutation

Question 13

How often do replication errors occur

Answer 13

1 in every 1* 10^8 base pairs

Question 14

How are errors minimalised?

Answer 14

There are enzymes that can proof read it incorrect neucleotides - reduce mutation rate

Question 15

What is the genetic code

Answer 15

The sequence of bases in dna

determines sequence of amino acids in the polypeptide

Question 16

What is the triplet code

Answer 16

3 based code for 1 amino acid in the protein

Each triplet is called a CODON

Question 17

What is a section of DNA that contains the sequence of bases/ codons to code for an entire protein ?

Answer 17

GENE

Question 18

Properties of the genetic code

Answer 18

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

Question 19

How many base triplets are possible ??

Answer 19

64

444

Question 20

Why is the genetic code non overlapping

Answer 20

DNA is read from base 1 rather than base 2 or 3

Question 21

Why is the genetic code degenerate

Answer 21

20 amino acids that occur in biological proteins regularly

Lot more codons than amino acids

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