Nucleic Acids And Nucleotides

Question 1

What does DNA stand for ?

Answer 1

Deoxyribonucleic acid

Question 2

What is the cell’s entire genetic content called?

Answer 2

The genome

Question 3

Name the components of a nucleic acid

Answer 3

-Pentose sugar
- nitrogen containing organic base
- phosphate group
- sugar-phosphate backbone
Bonds-
Condensation reaction to form phosphodiester bind

Question 4

Name the components of a DNA nucleotide ?

Answer 4

A deoxyribose sugar.
A phosphate group.
An organic base - adenine (A), cytosine (C), guanine (G), thymine (T).

Question 5

Name the components of RNA?

Answer 5

Ribose sugar
A phosphate group.
An organic base - adenine (A), cytosine (C), guanine (G), uracil (U).

Question 6

Describe DNA

Answer 6

A DNA molecule is a double helix made up of two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs.
The two polynucleotide strands are antiparallel because they run in opposite directions.

Question 7

What is complementary base pairing

Answer 7

Guanine can pair with Cytosine (G-C)
Adenine can pair with Uracil (A-U)
Adenine can pair with Thymine (A-T)

Question 8

Semi-conservative replication

Answer 8

Bases match in complementary base pairing
On original strand is conserved in semi conservative replication
DNA polymerase forms the new DNA strand
DNA helicase breaks the hydrogen bonds in the DNA strand

Question 9

What bond is formed between adjacent nucleotides?

Answer 9

Phosphodiester

Question 10

How does ATP’s inorganic phosphate make other compounds more reactive?

Answer 10

Phosphorylation

Question 11

Describe transcription

Answer 11

Binding of rna polymerase

Question 12

Describe how polynucleotide strands are formed and broken down.

Answer 12

Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone).
Hydrolysis reactions use a molecule of water to break these bonds
Enzymes catalyse these reactions

Question 13

Describe the structure of DNA

Answer 13

Molecule twists to form DOUBLE HELIX of 2 deoxyribose polynucleotide strands (so there are 2 sugar-phosphate backbones)
H-BONDS form between COMPLEMENTARY BASE PAIRS (AT&GC) on strands that run antiparallel

Question 14

Name the purine bases and describe their structure

Answer 14

Adenine C5H5N5
Guanine C5H5N5O
Two-ring molecules

Question 15

Name the pyrimidine bases and describe their structure

Answer 15

Thymine
Cytosine
Uracil
One-ring molecules

Question 16

Why is DNA replication described as semi-conservative?

Answer 16

Strands from original DNA molecule after as templates
New DNA molecule contains 1 OLD STRAND & 1 NEW STRAND ( SPECIFIC BASE PAIRING enables genetic material to be CONSERVED accurately)

Question 17

Explain the role of DNA helicase in semiconservative replication ?

Answer 17

Breaks H-bonds between base pairs to form 2 single strands, each of which can act as a template

Question 18

How is a new strand formed during semi-conservative replication?

Answer 18

1. Free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
2. DNA POLYMERASE joins adjacent nucleotides on new strand in a 5’ => 3’ direction via condensation reactions to form phosphodiester bonds
3. H-bonds reform

Question 19

Identify features of the genetic code.

Answer 19

• NON-OVERLAPPING
  Each triplet is only read once
• DEGENERATE
  More than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids)
• universal
  Same bases and sequences used by all species

Question 20

Describe how DNA can be purified by precipitation

Answer 20

Add ethanol & a salt to aqueous solution
Nucleic acids precipitate out of solution
Centrifuge to obtain pellet of nucleic acid
Was pellet with ethanol & centrifuge again

Question 21

What does transcription produces and where does it occur?

Answer 21

Produces mRNA
Occurs in NUCLEUS

Question 22

Outline the process of transcription

Answer 22

1. RNA POLYMERASE binds to promoter region on a gene
2. Section of DNA uncoils (DNA GYRASE) into two strands with exposed bases (dna helicase)
   Antisense strand acts as template
3. Free nucleotides are attached to their complementary bases
4. RNA polymerase joins adjacent nucleotides to form PHOSPHODIESTER BONDS

Question 23

What happens after a strand of nRNA is transcribed?

Answer 23

-RNA polymerase detaches at terminator region
- H-bonds reform & DNA rewinds
- splicing removes introns from pre-mRNA in eukaryotic cells
- mRNA moves out of nucleus via nuclear pore & attaches to ribosome

Question 24

What does translation produce and where does it occur?

Answer 24

Produces proteins
Occurs in cytoplasm on ribosomes (which are made of protein+ rRNA)

Question 25

Outline the process of translation

Answer 25

1. Ribosome move along mRNA until ‘start’ codon
2. tRNA anticodon attaches to complementary bases on mRNA
3. Condensation reactions between amino acids on tRNA form peptide bonds. Requires energy from ATP hydrolysis
4. Process continues to form polypeptide chain until ‘stop’ codon is reached

Question 26

What is a mutation?

Answer 26

An alteration to the DNA base sequence.
Mutations often arise spontaneously during DNA replication - deletion, insertion , substitution