DNA and meiosis

Question 1

Base structure

Answer 1

Single ring: Cytosine, Thymine Double ring: Guanine, Adenine Pairs: C&G, A&T

Question 2

Organic base bonds

Answer 2

A&T two hydrogen bonds

C&G three hydrogen bonds

Question 3

Nucleotide structure

Answer 3

Phosphate group

Deoxyribose

Organic base

Question 4

Direction of the polynucleotides

Answer 4

They run antiparallel to each other

Question 5

DNA adaptations for function

Answer 5

• Hydrogen bonds give stability en masse, but are easy to seperate for replication and protein synthesis
• Very stable so it can be passed for generations without change
• Extremely large to carry an immense amount of genetic information
• The helical cylinder of the deoxyribose-phosphate backbone protects the base pairs from corruption by physical/chemical forces

Question 6

Triplet Code- how it was calculated

Answer 6

• There are 20 amino acids and four bases which can code for these bases
• If pairs of bases coded for amino acids, only 16 amino acids could exist (4x4)
• Therefore three base combinations must code fore amino acids as this gives a potential of 64 (4x4x4) codes.
• Some amino acids must therefore have more than one code

Question 7

Eukaryotic nuclear DNA

Answer 7

Eukaryotes have large, linear DNA molecules. They associate with proteins to form chromosomes. Much of it does not code for amino acids and these sections are called introns. They occur within genes and as repeats between genes

Question 8

Start and stop codes

Answer 8

There is one start code amino acid, methionine

THere are three stop codes which mark teh end of a polypeptid chain

Question 9

Reading the code

Answer 9

It is non-overlapping, so each base is read only once. eg/ 1234567 is read as 123, 456, while 7 does not form an amino acid. It is univeral, so it is the same in all organisms.

Question 10

Genes and alleles

Answer 10

A gene is a characteristic, such as eye colour. An allels is the version of the gene, such as blue and brown.

Question 11

Prokaryotic vs Eukaryotic DNA

Answer 11

• Prokaryotes do not conain chromosomes as their DNA forms a cirlce and is not associated with protein molecules
• Eukaryotes have larger, linear DNA molecules. They associate with proteins to form chromosomes

Question 12

Homologous Chromosomes

Answer 12

Gaining 23 chromosomes from each parent gives us the diploid number (46 in humans). Each one from the egg is a pair to one form the sperm, and this is called a homologous pair.

Question 13

Chromosome structure

Answer 13

Question 14

Meiosis definiton

Answer 14

Produces four daughter nuclei, each with half the number of chromosomes as the parent cell. These are gametes.

Question 15

Independant segregation

Answer 15

The combination of chromosomes in a daughter cell is random as the homologous pairs line up randomly.

Question 16

Crossing over and recombination

Answer 16

• During meiosis 1, the chromatids of each pair become twisted around each other.
• Portions of the chromatids break off and rejoin to the chromatids of its homologous partner.

Question 17

Intron

Answer 17

A section of DNA which doesn’t code for anything