DNA and Nucleotides

Question 1

what are nucleic acids

Answer 1

• large molecule in the nuclei
• DNA
• RNA
• made of carbon, hydrogen, oxygen, nitrogen, phosphorus

Question 2

what is the structure of a nucleotide

Answer 2

• phosphate group
• pentose sugar
• nitrogenous base

Question 3

what is the structure of deoxyribonucleic acid (DNA)

Answer 3

• deoxyribose sugar
• 1 less oxygen than ribose
• adenine, thymine, guanine , thymine
• adenine - thymine = 2 hydrogen bonds
• guanine - cytosine = 3 hydrogen bonds

Question 4

what are purines and pyrimidines

Answer 4

purines
- single carbon ring structure
- guanine, adenine

pyrimidines
- double carbon ring structure
- cytosine, thymine

Question 5

what is a double helix

Answer 5

• two strands are held together by hydrogen bonds
• strands are antiparallel (5 to 3) (3 to 5)
• each polynucleotide is made up of altering deoxyribose sugars and phosphate group bonded by phosphodiester bonds to form sugar-phosphate backbone

Question 6

what is base pairing

Answer 6

• complementary
• small pyrimidine base pairs with large purine base to maintain a constant distance between DNA backbones

Question 7

what is ribonucleic acid (RNA)

Answer 7

• ribose sugar
• phosphate group
• adenine, cytosine, guanine, uracil
• single polypeptide chain

Question 8

what is the phosphodiester bond

Answer 8

• condensation between two nucleotides form the bond
• synthesis and breakdown of polynucleotides requires the formation of phosphodiester bonds

Question 9

what are phosphorylated nucleotides

Answer 9

Adenosine triphosphate (ADP)
Adenosine diphosphate (ATP)

Question 10

describe the process of phosphorylating nucleotides

Answer 10

• ATP provides energy for chemical reactions
• ATP synthesised from ADP and Pi using energy
• ADP phosphorylated to form ATP and phosphate bond
• energy stored in phosphate bond
• when energy is needed ATP is broken back into ADP and Pi
• energy released from the phosphate bond and is used

Question 11

describe the process of DNA purification

Answer 11

• grind sample with mortar and pestle - breaks down the cell walls
• mix sample with detergent - breaks down cell membrane releasing cell content into solution
• add salt - breaks hydrogen bonds
• place in a water bath at 60 for 15 mins - stops enzyme from working
• filter mixture
• add protease enzyme - breaks down proteins in the nuclei
• add ethanol - DNA precipitate out of the solution

Question 12

describe the process of semi-conservative replication

Answer 12

• DNA helicase breaks hydrogen bonds between polynucleotide strands
• each original strand acts as a template for a new strand
• free floating DNA nucleotides join to the exposed bases on each original strand
• nucleotides are joined by DNA polymerase
• forms sugar phosphate backbone
• hydrogen bonds form and strands twist
• each new strand has one original strand

Question 13

what is DNA helicase

Answer 13

• travels along DNA backbone catalysing reactions that break hydrogen bonds between complementary base pairs

Question 14

what is DNA polymerase

Answer 14

• catalyses the formation of phosphodiester bonds between freely exposed bases

Question 15

what is the genetic code

Answer 15

• a gene is a sequence of nucleotides that form part of a DNA molecule
• codes for the production of a specific polynucleotide

Question 16

what is a triplet code

Answer 16

• sequence of 3 bases - codon
• each codon codes for an amino acids
• genetic code

Question 17

what is the degenerate code

Answer 17

• 64 different codons possible
• start and stop codon
• some amino acids are coded for by more than one base triplet

Question 18

how is DNA copied

Answer 18

• DNA is found in the nucleus
• organelles that make proteins are in the cytoplasm
• section of DNA is copied into mRNA
• mRNA joins with a ribosome to synthesise a protein

Question 19

what is messenger mRNA

Answer 19

• Made in the nucleus
• three adjacent bases
• carries genetic code from DNA in the nucleus to the cytoplasm to make a protein during translation

Question 20

what is transfer RNA

Answer 20

• found in the cytoplasm
• amino acid binding site at one end and anticodon at another end
• carries amino acid used to make proteins to the ribosomes

Question 21

what is ribosomal RNA

Answer 21

• forms 2 subunits in a protein
• ribosome moves along the mRNA strand during protein synthesis
• helps to catalyse the formation of peptide bonds

Question 22

describe the processes of transcription

Answer 22

• RNA polymerase attaches to DNA double helix at the start of a gene
• hydrogen bonds break and uncoil strand
• 1 strand acts as a template to form mRNA strand
• RNA polymerase lines up free RNA nucleotides causing base pairing
• nucleotides are joined together
• RNA polymerase moves along the DNA separating the strands and assembling mRNA
• hydrogen bonds re-form once RNA polymerase has passed
• RNA polymerase reaches a stop codon, stops making mRNA and detaches from DNA
• mRNA moves out of the nucleus

Question 23

describe the process of translation

Answer 23

• mRNA strand attaches to a ribosome and tRNA carries amino acids to ribosome
• tRNA molecule with anticodon complementary to start codon on the mRNA attaches
• second tRNA molecule attaches itself to the next codon
• rRNA catalyses the formation of peptide bond joining together amino acids attached to tRNA
• first tRNA molecule leaves and leaves amino acids behind
• third tRNA molecule binds to the next codon
• amino acids binds and second molecule moves
• process continues until it reaches a stop codon
• polypeptide chain moves away from the ribosome