Nucleic acids

Question 1

How many DNA Bases code for a single amino acid

Answer 1

3

Question 2

How many different combinations of amino acids are there

Answer 2

4(3) - 64 combinations

Question 3

What happens to the remaining combinations of amino acids

Answer 3

• several codons can code for one amino acid
• some used for start/stop/termination
• mutation results in a change in amino acid and a new one can easily be inserted

Question 4

What is the definition of a gene

Answer 4

a gene is a section of DNA that codes for the production of a polypeptide

Question 5

What is semi-conservative replication

Answer 5

One strand from original strand and one strand newly formed

Question 6

Describe the process of transcription briefly

Answer 6

• DNA/ gene copied and transcribed into mRNA
• free activated (RNA) nucleotides
• line up by complimentary base pairing
• Catalysed by RNA polymerase

Question 7

Describe briefly process of translation

Answer 7

• Mrna moves to ribosomes
• tRNA binds to mRNA
• anticodons bind to codons
• complimentary amino acid attaches to tRNA
• formation of peptide bond between amino acids

Question 8

What is the importance of complimentary base pairing

Answer 8

• DNA can be replicated without error / same sequence of amino acids produced
• reduces occurrence of mutation
• allows formation of hydrogen bonds

Question 9

How is the glucose molecule well suited to its function

Answer 9

• soluble so can easily be transported around the organism
• small - can easily diffuse across cell membranes
• easily broken down to release energy
• molecules can join alpha glucose molecules to form maltose (named disaccharides)

Question 10

Describe the structural relationship between deoxyribose and the other components of the
DNA molecule.

Answer 10

• part of a nucleotide
• bonded to base and phosphate
• phosphate joined to C5/C3 base at C1
• part of backbone of DNA
• links to next phosphate on adjacent nucleotide
• nucleotide is a monomer of DNA

Question 11

How does a DNA molecule replicate

Answer 11

• semi-conservative replication
• double helix unwinds
• hydrogen bonds between bases break
• each strand acts as a template for the formation of a new molecule
• free nucleotides align with exposed bases
• complimentary base pairing/ purine to pyrimidine
• hydrogen bonds reform
• sugar phosphate reforms /adjacent nucleotides join
• DNA polymerase joins backbone/strands
• each new molecule has one old strand and one new

Question 12

How is information coded on genes is used to synthesis a polypeptide

Answer 12

• synthesis
• DNA, copied into /, mRNA or described ;
• transcription / transcribed ;
• one strand copied ;
• complementary base-pairing ;
• triplet code / code read in threes / codon is 3 bases ;
• base sequence determines amino acid sequence ;
• translation ;
• ribosomes ;
• role of tRNA described

Question 13

How do polypeptides control the physical development of an organism

Answer 13

• haemoglobin e.g
• enzyme reactions/metabolism
• hormones
• receptors
• turning genes on/off

Question 14

How does the structure of DNA allow it to function

Answer 14

-double stranded
-each strand acts as a template
-hydrogen binds easily break/form between bases
-complimentary base pairs
- purines can only pair with pyrimidines due to diff sizes giving equal sized rungs on the ladder
-Hydrogen bonding A-T = 2
C-G=3

Question 15

What happens if the sequence of nucleotides change

Answer 15

• there is a different combination of amino acids
• different tertiary structure
• cant perform specific function

Question 16

What supplies the energy for phosphodiester bonds

Answer 16

hydrolysis of activated nucleotides in the nucleoplasm

Question 17

How to prokaryotes/mitochondria/chloroplasts replicate

Answer 17

• bubble sprouts
• unwinds/unzips
• complimentary bases join to exposed nucleotides
• eventually whole loop is copied

Question 18

What is the complimentary base pairs

Answer 18

purines always pair with pyrimidines so rungs on the ladder are always the same length

Question 19

Purines and pyrimidines

Answer 19

-purines - double ringed A+G
-Pyrimidines - single ringed - C+T
contains nitrogen

Question 20

What is the difference between ribose and deoxyribose

Answer 20

deoxyribose contains an H instead of an OH

Question 21

What is the meslston and Stahl experiement

Answer 21

proof of semi - conservative replication
1st - heavy as old DNA
2nd - 1X heavy 1x light
3rd- 1x hevay 2x light

Question 22

semi conservative replication (in detail)

Answer 22

• DNA starts as a double helix, DNA gyrase - untwists
• DNA helicase unzips - breaks hydrogen bonds
• single stranded binding proteins attach to prevent reanneling (binding back together)
• DNA polymerase binds to the leadign strand and forms covalent phosphodiester bonds at the start of the replication fork
• moves in a 5’ 3’ direction
• free nucleotides in nucleoplasm fly in and attach via complimentary base pairs
• lagging strand synthesised discontinuously
• DNA ligase closes the gaps in the backbone
• each new strand consists of one old strand and one new

Question 23

What does mRNA consist of

Answer 23

• contains ribose

- contains uracil

Question 24

process of transcription (detail)

Answer 24

• gene unwinds/unzips
• hydrogen bonds break
• DNA polymerase catalyses the formation of temp hydrogen bonds between RNA and DNA bases on template strand
• coding strand produced complimentray to template strand

Question 25

What are ribosomes made up of

Answer 25

• 2 subunits one large and one small

- protein and rRNA

Question 26

What are the features of the genetic code

Answer 26

• universal - same in all organisms

- degenerate - multiple codes for one amino acid

Question 27

process of transcription (detail)

Answer 27

• small subunit of rRNA binds to mRNA then large
• hydrogen bonds temporarily form
• tRNA binds to amino acids in cytoplasm which then is brought to mRNA
• complimentary base pairing between anti codon and codon
• peptide bonds from between two amino acids
• ribosmome moves along and a new tRNA comes in with anticodon
• peptide bond forms and continues till STOP codon is reached

Question 28

Structure of tRNA

Answer 28

These tRNA molecules have a triplet of unpaired bases at one end (known as the anticodon) and a region where a specific amino acid can attach at the other
There are at least 20 different tRNA molecules, each with a specific anticodon and specific amino acid binding site

Question 29

function of tRNA

Answer 29

The tRNA molecules bind with their specific amino acids (also in the cytoplasm) and bring them to the mRNA molecule on the ribosome
The triplet of bases (anticodon) on each tRNA molecule pairs with a complementary triplet (codon) on the mRNA molecule
Two tRNA molecules fit onto the ribosome at any one time, bringing the amino acid they are each carrying side by side