Nucleic Acids, 2.3

Question 1

What is a nucleotide?

Answer 1

A monomer

Question 2

What is nucleic acid?

Answer 2

Long polymer made from repeating units

Question 3

What are nucleotides composed of?

Answer 3

Phosphate, Five-Carbon Sugar and a nitrogenous base

Question 4

What is the bond between the nucleotide bases called?

Answer 4

Phosphodiester

Question 5

Name two purine bases

Answer 5

Adenine. Guanine.

Question 6

Name three pyrimidine bases

Answer 6

Thymine. Cytosine. Uracil.

Question 7

Which bases bind together?

Answer 7

A and T. A and U. T and C.

Question 8

When are they phosphorylated nucleotides?

Answer 8

When they contain more than one phosphate group eg ADP

Question 9

What are the 2 forms of nucleic acids?

Answer 9

DNA - deoxyribose nucleic acid. RNA - ribonucleic acid.

Question 10

Why is DNA important?

Answer 10

It makes up the structure of living organisms

Question 11

What is the structure of DNA?

Answer 11

Consists of two strands of polynucleotides that are anti parallel. Arranged in a double helix.

Question 12

What reaction are nucleotide bonds formed by?

Answer 12

Condensation reaction

Question 13

What is the antiparallel sugar phosphate backbone?

Answer 13

The strands run in different directions but are parallel. One runs from 3’ end to 5’ and the other runs from 5’ to 3’

Question 14

What bonds are the anti parallel strands held together by?

Answer 14

Hydrogen

Question 15

How many hydrogen bonds are between A and T?

Answer 15

2

Question 16

How many hydrogen bonds are between C and G?

Answer 16

3

Question 17

What is meant by complementary base pairing?

Answer 17

Each base can only join with another particular base

Question 18

What is meant by a double helix?

Answer 18

When two polynucleotide strands are twisted into a spiral and held together by hydrogen bonds

Question 19

What is DNA wrapped around?

Answer 19

Histone proteins`

Question 20

How is DNA arranged in prokaryotes?

Answer 20

In a loop not enclose in a nucleus. Described as naked

Question 21

Name the differences between RNA and DNA.

Answer 21

RNA has Uracil instead of Thymine. RNA is a single stranded polynucleotide.

Question 22

When does DNA replication occur?

Answer 22

During interphase

Question 23

Describe the different stages of DNA replication.

Answer 23

1. Unwind - double helix is untwisted
2. Unzips - hydrogen bonds broken by DNA Helicase
3. Free nucleotide bases bond to exposed bases
4. DNA Polymerase catalyses the addition of new bases, using the DNA strand as a template
5. Leading strand synthesized continuously
6. Lagging strand synthesized in fragments

Question 24

What does the hydrolysis of activated nucleotides release?

Answer 24

Extra phosphate groups. Supplies energy for the phosphodiester bond

Question 25

Define semi conservative replication

Answer 25

DNA replicates and has one new strand and one old strand, the two strands are identical.

Question 26

Why is DNA replication important?

Answer 26

Ensures the preservation of genetic information. Structure and functions of proteins relies entirely on the correct sequence being copied,

Question 27

What is the proof for semi conservative replication?

Answer 27

1. Heavy 15N - grown for 14 generations 2. Mixed with lighter 14N - undergo one replication 3. Turned out to be a hybrid of both 4. Allowed to replicate once more 5. When centrifuged showed two different bands - one hybrid one light

Question 28

What does complementary base pairing allow?

Answer 28

Replication. The code to be preserved.

Question 29

Key features of the genetic code.

Answer 29

Sequence of 3 bases. Contains thousands of genes each codes for a specific polypeptide. Is universal. Degenerate.

Question 30

What is the triplet code?

Answer 30

A sequence of 3 bases which codes for an amino acid

Question 31

What does degenerate mean?

Answer 31

Amino acid can be coded for by more than one triplet code

Question 32

Why does a polypeptide need the correct primary structure?

Answer 32

So it will fold correctly and will be able to carry out its function

Question 33

What is transcription?

Answer 33

Making mRNA from a DNA template

Question 34

What is translation?

Answer 34

Formation of proteins at a ribosome using mRNA

Question 35

Which strand of DNA is the mRNA formed from?

Answer 35

The template strand - it's identical to the coding strand

Question 36

Describe the stages of transcription

Answer 36

1. DNA unwinds and unzips- DNA Helicase 2. RNA polymerase catalyses the formation of a complementary mRNA strand from free RNA nucleotides 3. As the mRNA strand is formed the DNA recoils behind 4. mRNA passes out of the nucleus and attaches to a ribosome

Question 37

What are the key features of tRNA?

Answer 37

Carry specific amino acids. Have an anticodon that binds to complementary codon on mRNA. Has 3 unpaired bases for amino acid to join.

Question 38

What is the start codon?

Answer 38

AUG

Question 39

Describe the stages of translation

Answer 39

1. mRNA attaches to the start codon on a ribosome 2. tRNA binds to complementary codon on mRNA 3. tRNA carries an amino acid 4. Another tRNA attaches and there are now 2 amino acids 5. The amino acids form a polypeptide bond 6. This continues until the stop codon is reached