Topic 1.3 Nucleotides

Question 1

The nucleotide

Answer 1

-Nucleotides are monomers of Nucleic acids (DNA and RNA)
-A nucleotide is composed of:
-a pent sugar (DNA-deoxyribose, RNA-ribose)
-an organic Nitrogenous base
-a phosphate group

Question 2

Base groups: Purines

Answer 2

Adenine (DNA+RNA)
Guanine (DNA+RNA)
-Longer as the contain two nitrogenous rings

Question 3

Base groups: Pyrimidines

Answer 3

Cytosine (DNA+RNA)
Thymine (DNA only)
Uracil (RNA only)
-Smaller as they only contain are nitrogenous ring

Question 4

Deoxyribose Nucleic Acid

Answer 4

-Double helix structure
-Pentose sugar: deoxyribose
-Bases:
-adenine
-thymine
-guanine
-cytosine
-Base pairs: AT CG
-Held together by hydrogen bonds (weak but extensive)

Question 5

Ribonucleic Acid

Answer 5

-Single stranded and linear structure
-Pentose sugar: ribose
-Bases:
-adenine
-cytosine
-guanine
-uracil
-Base pairs: AU CG

Question 6

Central Dogma in genetics

Answer 6

DNA—>RNA—>Protein

Question 7

ATP

Answer 7

-Adenosine triphosphate (nucleotide)
-Three phosphate groups
-ATP is made during respiration
-Condensation reaction (ATP synthase)
ATP + H2O –> ADP + Pi
-Opposite reaction: hydrolysis (ATP hydrolase)

Question 8

ATP process (5)

Answer 8

1. ATP releases small, manageable amounts so no energy is wasted
2. ATP is a small and soluble molecules easily transported around the cell
3. Only one bond is broken/hydrolysed to release energy, which is why energy release is immediate
4. It can transfer energy to another molecule by transferring one of its phosphate groups
5. ATP can’t pass out of the cell, the cell laws has an immediate supply of energy
   (all cells need to respire so they can produce ATP)
   ATP ⇌ ADP + Pi
   (–>hydrolysis <–condensation

Question 9

Semi-conservative replication (4)

Answer 9

1. DNA helices unwinds/unzips the double stranded DNA by breaking the hydrogen bonds
2. This produces two single-stranded DNA template
3. New DNA nucleotides now join with their specific complimentary base on the template strand
4. These are joined by DNA polymerase (has ‘proof reading’ abilities; checks for mistakes) making sure no mutation occurs

Each daughter cell has:
-one original strand (conserved)
-one new strand

Question 10

A gene

Answer 10

A gene is a sequence of DNA base which codes for a sequence of amino acids to form a protein.

Question 11

Genetic code

Answer 11

The sequence of triplets which codes for the sequence of amino acids
-Three bases on DNA codes for one amino acid

Question 12

Genetic code rules: Universal

Answer 12

The same triplet/codons code for the same amino acid in all organisms.

Question 13

Genetic code rules: Degenerate

Answer 13

More than one triplet can code for a particular amino acid.
(There are more codons than amino acids so some aminos acids are coded for by more than one codon).

Question 14

Genetic code rules: Non-overlapping

Answer 14

Three codons are always read together in order.

Question 15

Start codons

Answer 15

DNA: TAC
mRNA: AUG

Question 16

Stop codons

Answer 16

DNA: ATC AGT ATT
mRNA: UAG UGA UAA

Question 17

Transcription (nucleus) (6)

Answer 17

1. DNA helicase unwinds and unzips the DNA by breaking hydrogen bonds between bases
2. RNA polymerase binds to the non-coding region of DNA up from the gene to be transcribed
3. RNA polymerase reaches the coding region of the gene and starts making a copy of the template strand (anti-sense strand)
4. RNA nucleotides are joined by phosphodiester bonds to form pre-mRNA strand
5. The RNA splicing occurs which cuts out introns and joins the exons to form mRNA
6. The mRNA leaves the nucleus via a nuclear pore and enters the cytoplasm.

Question 18

Translation (ribosome) (6)

Answer 18

1. mRNA attaches to a ribosome in the cytoplasm, two codons at a time (a codon- three bases)
2. A tRNA molecule with the complimentary anti-codon binds to the codon
3. The amino acids join together to start forming a polypeptide by a peptide bond
4. The ribosome moves down the mRNA one codon at a time and another amino acid is joined to the polypeptide
5. The polypeptide then folds into shape to form a protein eg. enzyme, haemoglobin
6. The protein has a specific shape determined by the order of the amino acids.

Question 19

Intron

Answer 19

A sement of DNA or RNA molecule which doesn’t code for proteins and interrupts the sequence of genes.

Question 20

Exon

Answer 20

A segment of DNA or RNA molecule containing information coding for a protein or peptide sequence.

Question 21

Protein synthesis ‘equation’

Answer 21

DNA ———–> mRNA ———–> Protein
(transcription) (translation)

Question 22

Post translational modification (PTM)

Answer 22

-When the protein has made it is not always functional; inactive
-It undergoes PTM is the Golgi body
-eg. insulin 100 amino acids undergoes extensive PTM to produce active insulin which is 51 amino acids long

Question 23

Mutation: Substitution

Answer 23

One base is substituted for another
ie. the wrong base is inserted
(change in primary structure; change in 3D tertiary structure; different hydrogen bonding; no enzyme-substrate formed; non-functioning protein)

Question 24

Mutation: Addition

Answer 24

An extra base is added to the sequence (frame shift)
All the triplets after the addition will shift
Produces a major change in the protein because its a totally different primary sequence.

Question 25

Mutation: deletion

Answer 25

A base is removed from the sequence. This also causes a frame shift.

Question 26

What causes mutations?

Answer 26

-Random occurrence -Ionising radiation eg. UV light, X-rays etc -Chemicals called mutagens eg. mustard gas, chemical,ls in cigarette smoke.

Question 27

Chromosomal mutation

Answer 27

An extra copy of a chromosome eg. Downs syndrome- 3 chromosome 21s (an extra)

Question 28

How do polynucleotide strands form?

Answer 28

Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)

Question 29

How is a new strand formed during semiconservative replication?

Answer 29

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 30

Structure of mRNA

Answer 30

-Long ribose polynucleotide with sugar- phosphate backbone -Single stranded and linear (no H bonds between complementary base pairs) -Codon sequence is complimentary to axons of 1 gene from 1 DNA strand.

Question 31

Structure of tRNA

Answer 31

-Single strand folded into clover shape (some paired bases) -Anticodon on one end, amino acid binding site on the other -

Question 32

Antisense strand

Answer 32

Template of DNA which is transcribed.

Question 33

Sense strand

Answer 33

Strand with the same base sequence as mRNA (but with thymine instead of uracil)

Question 34

What happens after a strand of mRNA is transcribed?

Answer 34

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

Question 35

State the role of ATP during translation

Answer 35

ATP hydrolysis provides energy to form peptide bonds.

Question 36

What is sickle cell anaemia?

Answer 36

Genetic condition that results in abnormal haemoglobin. Impaired ability to transport oxygen= rapid heart rate, fatigue dizziness. Sickle shaped red blood cells 'stick' in vessels.

Question 37

What causes sickle cell anaemia in humans?

Answer 37

Missense point mutation in gene that codes for β strand in haemoglobin. Change in primary structure= different tertiary structure. Abnormal haemoglobin molecules form strands that make red blood cells sickle shaped.