1.5 Nucleic acids and their functions

Question 1

What does a nucleotide consist of?

Answer 1

• Pentose sugar
• phosphate
• nitrogenous base

Question 2

What does DNA mean?

Answer 2

Deoxyribonucleic acid

Question 3

What is the name of the sugar and the bases of DNA?

Answer 3

Sugar: Deoxyribose
Bases: Adenine, Thymine, Guanine, Cytosine

Question 4

What does RNA mean?

Answer 4

Ribonucleic acid

Question 5

What is the name of the sugar and the bases of RNA?

Answer 5

Sugar: Ribose
Bases: Adenine, Uracil, Guanine, Cytosine

Question 6

What does ATP mean?

Answer 6

Adenosine triphosphate

Question 7

What does ATP consist of?

Answer 7

Sugar: Ribose
Base: Adenine
+ 3 phosphate heads

Question 8

How is ATP formed?

Answer 8

In an endergonic reaction (a reaction that uses energy)

Question 9

What is the process of ATP forming?

Answer 9

• ADP and phosphate are combined
• energy to form bond comes from exergonic energy from respiration
• this is a condensation reaction as water in eliminated and the bond is formed
• catalyst for reaction: ATP synthetase

Question 10

Why is ATP known as the universal energy currency?

Answer 10

It provides energy to all reactions to all cells in all species

Question 11

What are the purine bases?

Answer 11

Adenine and Guanine

Question 12

What is a purine base?

Answer 12

a double ring structure

Question 13

What are the pyrimidine bases?

Answer 13

Thymine, Cytosine and Uracil

Question 13

What is a pyrimidine base?

Answer 13

a single ring structure

Question 14

What are the complimentary base pairs?

Answer 14

Adenine - Thymine (uracil in RNA)

Cytosine - Guanine

Question 15

What are the two functions of DNA?

Answer 15

• base sequence codes for amino acid sequences in protein synthesis
• replicating prior to cell division so each daughter cell gets equal DNA

Question 16

What is the structure of DNA?

Answer 16

• two complimentary polynucleotide strands
• sugar - phosphate molecules joined by condensation reaction
• sugar-phosphate molecules form ‘backbone’ of the molecule
• bases joined by hydrogen bonds form the ‘rungs’ in the middle
• double helix structure

Question 17

What is the structure of RNA?

Answer 17

• single stranded polynucleotide
• pentose sugar ribose
• shorter than DNA
• bases present: Adenine, uracil, guanine and cytosine

Question 18

What is rRNA?

Answer 18

Ribosomal RNA - made in the nucleolus, component of ribosome. Single polynucleotide folded into globular structure

Question 19

What is tRNA?

Answer 19

Transfer RNA - Single stranded polynucleotide twisted into clover leaf shape. Carries amino acids to ribosomes.

Question 19

What is mRNA?

Answer 19

Messenger RNA - made in nucleus, three bases code for one amino acid. Carries code from DNA in nucleus out the nuclear pore and into cytoplasm where mRNA then attaches to ribosomes

Question 20

What are the steps to extracting DNA from cells?

Answer 20

1. crush the source cells in detergent, salt and water to release DNA
2. Filter cell debris and collect extract
3. Pour ice cold alcohol down the tube containing extract
4. DNA precipitates at the juntion of the extract and alcohol
5. CNA can be stained red using acetic orcein

Question 21

What does Meselson and Stahl’s experiment propose?

Answer 21

1. Conservative replication
2. Dispersive replication
3. Semi-conservative replication

Question 22

What is conservative replication?

Answer 22

DNA molecule is copied from the original, leaving the original as it was

Question 23

What is semi-conservative replication?

Answer 23

two polynucleotide chains would part, new nucleotides attach to each of the chains, new molecule nowhas one old and one new chain

Question 24

What is dispersive replication?

Answer 24

Sections of DNA molecule are copied and spliced together making each new DNA molecule a mix of original and new

Question 25

How did Meselson and Stahl conduct their experiment?

Answer 25

Meselson and Stahl used E.coli bacteria as the source of DNA. E.coli are easily grown in a flask of culture medium and replicate their cells (and DNA) every 20 minutes under optimal conditions.

Question 26

What did Meselson and Stahl discover with their experiment?

Answer 26

‘New’ and ‘original’ nucleotides were distinguished by the isotope of nitrogen (N) in the nitrogenous bases. 15N is heavier in mass than 14N, so DNA molecules containing bases with 15N and DNA molecules containing 14N can be separated by mass in centrifugation.

Question 27

Why is DNA said to be semi-conservative?

Answer 27

Consists of one original strand and one newly synthesised strand of DNA

Question 28

Where does 14N sit in the test tube?

Answer 28

At the top

Question 29

Where does 15N sit in the test tube?

Answer 29

At the bottom

Question 30

What is DNA Helicase and what does it do?

Answer 30

DNA Helicase is an enzyme that breaks hydrogen bonds holding the two polynucleotide chains together in DNA. 'Unzipping' DNA into two strands

Question 31

What is DNA Polymerase and what does it do?

Answer 31

DNA Polymerase is an enzyme that adds free nucleotides from nucleoplasm to exposed bases by forming H bonds between them

Question 32

What is DNA Ligase and what does it do?

Answer 32

DNA Ligase is an enzyme that rewinds the double helix of DNA

Question 33

What is the triplet code?

Answer 33

Three bases that code for a single amino acid

Question 34

What's the other name for the triplet code?

Answer 34

a codon

Question 35

What is Transcription?

Answer 35

The process of copying a segment of DNA into RNA.

Question 36

What is the process of transciprtion?

Answer 36

- DNA unzipped by DNA Helicase - RNA Polymerase attaches to DNA - Only one DNA strand is copied - Free RNA nucleotides align with their complimentary nucleotides on DNA strand - Bonds formed between the nucleotides - results in synthesis of mRNA - mRNA carries DNA code out the nucleus through nuclear pore to cytoplasm and attaches itself to a ribosome

Question 37

What happens when mRNA attaches itself to the ribosomes?

Answer 37

- ribosome read the DNA code on mRNA - tRNA attach to specific amino acids and carry them to the mRNA molecule - anticodon-codon bases align and a codon-anticodon complex is formed - Peptide bonds are formed between adjacent amino acids by condensation reaction