Module 2.1.3 Nucleotides Sambrook

Question 1

What are the purines in DNA?

Answer 1

Adenine
Guanine

DOUBLE ring structure

Question 2

What are the Pyrimidines ?

Answer 2

Thymine
Cytosine
Uracil

SINGLE ring structure

Question 3

Describe the structure of DNA

Answer 3

-DNA is made up of 2 complementary polynucleotide chains and the 2 strands are antiparallel.
-1 strand goes from 5’ to 3’ and the opposite strand goes from 3’ to 5’.
- hydrogen bonds hold the polynucleotide chains together.
- Ester bonds between the phosphate groups
- Hydrogen bonds between the nitrogenous bases
- this forms a double helix with major and minor grooves in an alternating pattern

Question 4

What are nucleotides in DNA ?

Answer 4

-building blocks of DNA
-Made of a deoxyribose Pentosesugar molecule with hydrogen at 2’ position, phosphate group and a nitrogenous base.
-hold the genetic material of DNA
- deoxyribose
THYMINE

Question 5

What is the significance of the nitrogenous base pairings in DNA ?

Answer 5

-Allows DNA to store and transmit genetic information.
-the specific pairing of the nitrogenous bases ensure that the genetic information is accurately copied during cell division.

Question 6

How does DNA replication occur ?

Answer 6

-2 complementary strands of the DNA molecule separate
-each strand acts as a template for the formation of a new complementary strand.

Question 7

How does the structure of DNA enable it to carry out its function?

Answer 7

1)Two strands = the DNA is stable
2)bases are inside the sugar phosphate back bone (spiral)= protected and the integrity of the genetic code is maintained
3)molecules are long = store a lot of genetic information
4) complementary base pairing = identical copies created

Question 8

What are the components of RNA nucleotides?

Answer 8

-ribose pentose sugar with a hydroxyl group at the 2’ position (making is more susceptible to hydrolysis)
-URACIL

Question 9

How many bonds are between adenine and thymine?

Answer 9

Two hydrogen bonds

Question 10

How many bonds are between guanine and cytosine?

Answer 10

3 hydrogen bonds

Question 11

What does helicase do?
(Step 1 of DNA replication)

Answer 11

-breaks down the hydrogen bonds between the 2 polynucleotide DNA strands.
-unzips helix.

Question 12

What do we mean by semi-conservative?

Answer 12

One strand of the DNA is new and one is original

Question 13

What direction does the leading strand go ?

Answer 13

3’ to 5’

Question 14

What direction does the lagging strand go ?

Answer 14

5’ to 3’

Question 15

What way does DNA polymerase move?

Answer 15

• in one direction
• 3’ to 5’
• on the original (template) strand

Question 16

What are okazaki fragments?

Answer 16

• Short sequences of DNA nucleotides on the lagging strand.
  -going in the wrong direction (away from the replication fork) so DNA polymerase synthasises the fragments in a discontinuous manner.

Question 17

What does Ligase do ?

Answer 17

Put the okazaki fragments together

Question 18

Stage one of DNA replication

Answer 18

1) DNA helicase breaks the hydrogen bonds between the 2 polynucleotide strands
The helix unzips to form 2 separate strands.

Question 19

What is stage 2 of dna replication ?

Answer 19

2) each original strand acts as a template for the new free floating DNA nucleotides to attach h at the complementary nitrogenous bases

Question 20

What is stage 3 of DNA replication?

Answer 20

3) DNA polymerase joins the nucleotides on the strands together
This forms a sugar phosphate backbone
Hydrogen bonds form between the nitrogenous bases on the new strands and original

Question 21

What is stage 4 of DNA replication ?

Answer 21

4) strands twist to form a double helix

Question 22

How do mutations occur ?

Answer 22

A change in the DNA base sequence

Question 23

What can happen if a mutation occurs?

Answer 23

They can alter the sequence of amino acids in a protein
Causing an abnormal protein to be produced

Question 24

What is genetic code non- overlapping?

Answer 24

Each codon ONLY codes for one amino acid
Base triplets don’t share their bases

Question 25

Why is the generic code degenerate?

Answer 25

different codons can encode for the same amino acid

Question 26

Why is genetic code universal?

Answer 26

All species use the same 4 nitrogenous bases ATCG each base codes for the same amino acid in all species

Question 27

What is the Role of tRNA ?

Answer 27

-Carries the amino acids that are used to make proteins to the ribosomes

Question 28

What is the role of mRNA?

Answer 28

-to deliver the genetic information from DNA to the ribosome to be translated into a protein

Question 29

What is the role of rRNA?

Answer 29

-helps catalyse the information of peptide between amino acids

Question 30

What is step one of transcription ?

Answer 30

1) rRNA polymerase attaches to the DNA at the beginning of a gene The hydrogen bonds break separating the strands The molecule uncoils with one of the strands being used as a template to make an mRNA copy

Question 31

What is step two of transcription?

Answer 31

2) RNA polymerase lines up free RNA nucleotides along the template strand u Complementary base paring means the mRNA strand ends up being a complementary copy of the DNA template (except T is U) RNA nucleotides pair up with specific bases forming mRNA

Question 32

What is the third stage of transcription?

Answer 32

3) RNA polymerase moves down the DNA, assembling the mRNA strand The hydrogen bonds reform with RNA polymerase and the strands twist again

Question 33

What is the fourth stage of transcription ?

Answer 33

4)RNA reaches a stop codon and stops producing mRNA and detaches itself from DNA moving out the nucleus through nuclear pores Attached to the ribosome I’m the cytoplasm

Question 34

What is the first stage of translation ?

Answer 34

1) tRNA carry amino acids to the ribosome The codon on the mRNA attaches itself to an anticodon on the tRNA

Question 35

What is the second stage of translation ?

Answer 35

2) the rNA in the ribosome catalyses the formation of a peptide bond between two amino acids The first tRNA moves away lwaving the amino acid behind This continues until a stop codon is reached on the mRNA molecule forming a polypeptide chain

Question 36

What are nucleotides made of

Answer 36

-pentose sugar. -nitrogenous base -phosphate group Elements: H,O,N and P

Question 37

What is DNA nucleotide made up of?

Answer 37

-Penrose sugar -> deoxyribose -phosphate group -nitrogenous base -> GCAT

Question 38

What is ADP made of?

Answer 38

-nitrogenous base -> adenine -pentose sugar-> ribose -TWO phosphate groups

Question 39

What is ATP made of ?

Answer 39

-nitrogenous base ->adenine -pentose sugar-> ribose -THREE phosphate groups

Question 40

Why does ATP and ADP have extra phosphate?

Answer 40

They have been phosphorylated

Question 41

How is ATP made?

Answer 41

Phosphorylated from ADP + P and a phosphate bond is formed during a condensation reaction creating ATP and water

Question 42

How is ATP released for use?

Answer 42

-energy is stored in phosphate bond -ATP is broken back down into ADP and P -energy is released from the phosphate bond

Question 43

Describe Polynucleotide structure

Answer 43

-join from phosphate group of one nucleotide and sugar of another -condensation reaction -phosphodiester bond is formed -> phosphate group and 2 ester bonds -chain -> sugar phosphate back bone

Question 44

What reaction is used to purify DNA ?

Answer 44

Precipitate reaction

Question 45

What does DNA do ?

Answer 45

-codes for sequence of amino acids in primary structure of protein determining its 3D structure

Question 46

How to purify DNA using precipitation.

Answer 46

1) homogenise the cell with a detergent 2)filter to remove large debris 3) add salt to break hydrogen bonds between DNA and water molecules 4) add protease to digest the proteins 5) add ice-cold ethanol to precipitate the DNA out the solution (white strands)

Question 47

What is a codon ?

Answer 47

-every 3 bases in the sequence that’s coded for an amino acid

Question 48

Where is mRNA found?

Answer 48

-made in nucleus -leaves into cytoplasm to go to ribosome

Question 49

Where is tRNA found?

Answer 49

Cytoplasm

Question 50

What is tRNA folded into ?

Answer 50

A clover leaf shape and bottom has 3 anticodons

Question 51

When does DNA replication occur?

Answer 51

S - phase in interphase