DNA structure & replication

Question 1

where do we find DNA eukaryotic cells

Answer 1

Bound to proteins (histones) in chromosomes in the nucleus (DNA + all the proteins associated with it (mainly histones) = chromatin).
Plus in chloroplasts and mitochondria.

Question 2

where do we find DNA in prokaryotic cells

Answer 2

As unbound circular DNA in the cytosol

Small rings of DNA called plasmids may also be present

Question 3

DNA replication

Answer 3

Base pairing allows each strand to serve as a template for a new strand. The new strand is half parent template and half new DNA. This is known as semi-conservative replication.

Question 4

stage 1 of replication: unwind DNA

Answer 4

Done by a helicase enzyme

Breaks the hydrogen bonds between the bases

This unwinds part of DNA helix, allowing the separation of the strands.

Question 5

stage 2: build daughter DNA strand

Answer 5

Add new complementary bases.

Done by the enzyme, DNA polymerase.

The enzyme moves 3′ to 5′ and can only add nucleotides to the 3′ end of a growing DNA strand.

Therefore the strand will grow 5′ → 3′.

Question 6

nucleic acids

Answer 6

Polymers

DNA and RNA are types of nucleic acid
§ deoxyribonucleic acid
§ ribonucleic acid

Individual unit called a nucleotide

Question 7

nucleic structure

Answer 7

Pentose sugar
§ Deoxyribose in DNA
§ Ribose in RNA

Phosphate group

Organic/nitrogenous base that always contains nitrogen

Question 8

nitrogenous bases

Answer 8

Purines
○ Adenine and Guanine
○ Double ringed structure*

Pyrimidines
○ Thymine and Cytosine
○ Single ringed structure*

Purines always pair with pyrimidines.
○ Paired by weak, base-specific hydrogen bonds between DNA strands.
○ A joins to T (2 hydrogen bonds) C joins to G (3 hydrogen bonds)