Ocr A Level Biology. 2.3 Nucleic Acids.

Front 1

What does DNA stand for?

Back 1

Deoxyribose nucleic acid

Front 2

What does RNA strand for?

Back 2

Ribonucleic acid

Front 3

What is the difference between DNA and RNA

Back 3

DNA contains deoxyribose sugar, RNA contains ribose sugar

Front 4

What is the monomer of polynucleotides?

Back 4

Nucleotides

Front 5

Describe the structure of a nucleotide?

Back 5

Made up of 3 parts

1. A phosphate group

2. A pentose sugar

3. An organic nitrogenous base

Front 6

How are the 3 parts of nucleotides joined together?

Back 6

By covalent bonds formed in condensation reactions

Front 7

What bases are found in DNA

Back 7

ATCG (Adenine, Thymine, Cytosine, Guanine)

Front 8

What bases are found in RNA?

Back 8

AUCG (Adenine, Uracil, Cytosine, Guanine)

Front 9

What is the structure of purine bases

Back 9

have 2 rings

Front 10

What is the structure of pyrimidine bases

Back 10

Have one rine

Front 11

Which bases are purine?

Back 11

Adenine, Guanine

Front 12

Which bases are pyrimidine

Back 12

Cytosine, Thymine, Uracil

Front 13

What bond is formed between nucleotides?

Back 13

A phosphodiester bond

Front 14

Describe the structure of DNA

Back 14

2 polynucleotide chains in antiparallel joined in a double helix structure.

Front 15

How are the chains in DNA held together?

Back 15

With hydrogen bonds formed via complementary base pairing (AT and CG)

Front 16

How many hydrogen bonds form between A and T?

Back 16

2

Front 17

How many hydrogen bonds form between C and G?

Back 17

3

Front 18

What 5 functions of DNA are caused by its structure?

Back 18

The sequence of bases is a code to build proteins.

Each long molecule stores lots of information.

The complementary base pairs can be replaced and easily copies.

Double helix gives the molecule stability.

Hydrogen bonds allow for easy unzipping for copying and reading information.

Front 19

What is a triplet code and what does it do?

Back 19

3 bases code for 1 amino acid

Front 20

Where does DNA replication begin

Back 20

At a replication fork (where two strands open and separate)

Front 21

What name is given to the process whereby DNA replicates?

Back 21

Semiconservative replication

Front 22

What is the combination of new or old strands in the daughter helix?

Back 22

Made up of 1 original strand and one newly synthesised strand

Front 23

Who proved the hypothesis of semiconservative replication?

Back 23

Meselsohn and Stahl

Front 24

What is the role of DNA gyrase in the first step of DNA replication?

Back 24

DNA gyrase uncoils the double helix to create a straight ladder like shape

Front 25

What is the role of DNA helicase in the second step of DNA replication?

Back 25

DNA helicase breaks the weak hydrogen bonds between complementary bases and strands separate at replication fork.

Front 26

What is the role of DNA polymerase in the 3rd step of DNA replication.

Back 26

DNA polymerase adds new ATP activated nucleotides to the exposed bases using complementary base pairing

Front 27

How does complementary base pairing occur on the lagging strand during DNA replication?

Back 27

in Okazaki fragments

Front 28

What is the function of DNA ligase in the 4th stage of DNA replication?

Back 28

DNA ligase helps join segments together by recreating the sugar phosphate backbone by recreating phosphodiester bonds between nucleotides

Front 29

What is the role of DNA polymerase at the same time as DNA ligase is functioning in the 4th stage of DNA replication?

Back 29

DNA polymerase proofreads the new DNA, checking for errors and repairing them, this is called excision repair.

Front 30

What is the role of DNA helicase in the final stage of DNA replication?

Back 30

DNA helicase recoils the 2, new identical DNA molecules which each consist of 1 old strand and 1 new strand

Front 31

How is DNA organised in eukaryotes

Back 31

Highly coiled and folded into chromosomes

The proteins around which DNA is coiled are Histone proteins

Loops of DNA can also be found in mitochondria

Front 32

How is DNA organised in prokaryotes

Back 32

DNA forms a long molecule in a complete circle

there are no histones

Prokaryotic cells can also contain plasmids

Front 33

What did Meselsohn and Stahl prove?

Back 33

Semiconservative replication

Front 34

They grew E.coli in heavy and light isotopes of what element?

Back 34

Nitrogen (N15 and N14)

Front 35

What are the two stages of protein synthesis?

Back 35

Transcription and translation

Front 36

Where does transcription take place?

Back 36

In the nucleus

Front 37

What enzyme is involved in transcription?

Back 37

RNA polymerase

Front 38

What is the product of transcription?

Back 38

A single strand of mRNA

Front 39

How does the mRNA exit the nucleus?

Back 39

Via a nuclear pore

Front 40

Where does translation take place?

Back 40

In the cytoplasm

Front 41

What is a codon?

Back 41

Each 3 bases of mRNA

Front 42

How many mRNA bases are exposed at a time when a ribosome attaches to the mRNA?

Back 42

6

Front 43

What happens in translation after the ribosome has attached to the mRNA?

Back 43

tRNA with the correct anticodon, and a specific amino acid attached to it, complementary base pairs with the mRNA codon to bring the specific amino acid to the ribosome.

Front 44

How does translation allow a polypeptide chain to form?

Back 44

The amino acids, which were brought to the ribosome by the tRNA, join via peptide bonds to form the start of a polypeptide chain.

Front 45

What is the start codon?

Back 45

AUG

Front 46

How many stop codons are there?

Back 46

3

Front 47

What happens when a stop codon is reached?

Back 47

The ribosome stops translating

Front 48

What would happen if a mutation caused a stop codon to appear early?

Back 48

A truncated protein would be produced