nucleotides and nucleic acids

Question 1

structure of nucleic acid

Answer 1

large molecule with 2 parts - backbone of alternating sugar and phosphate molecules bonded in long chain by phosphodiester bonds - each sugar group in backbone attached to nucleotide base

Question 2

types of nucleic acid

Answer 2

DNA, mRNA, tRNA, rRNA

Question 3

bases in DNA

Answer 3

adenine - thymine
guanine - cytosine

Question 4

bases in RNA

Answer 4

adenine - uracil
guanine - cytosine

Question 5

pyramidine bases

Answer 5

cytosine, thymine, uracil

Question 6

purine bases

Answer 6

adenine, guanine

Question 7

how are phosphodiester bonds formed in DNA

Answer 7

DNA ligase catalyses formation of phosphodiester bonds between phosphate groups of 1 nucleotide and sugar of another

Question 8

how is energy released by ATP

Answer 8

ATP is hydrolysed to APP and Pi (inorganic phosphate) releasing 30.6kJ of energy

Question 9

DNA replication steps

Answer 9

1. unwinding and unzipping DNA strands
2. free nucleotides bind
3. DNA polymerase joins
4. DNA fragments sealed up

Question 10

first step of DNA replication

Answer 10

DNA gyrase unwinds, DNA helicase unzips strands by breaking H bonds between base pairs

Question 11

second step of DNA replication

Answer 11

replication fork formation revealed and free nucleotides are attracted to bases

Question 12

third step of DNA replication

Answer 12

activated nucleotides are joined by DNA polymerase by strong covalent bonds which reforms phosphate sugar backbone

Question 13

fourth step of DNA replication

Answer 13

DNA fragments sealed by DNA ligase resulting in two DNAs each with one new strand and one original

Question 14

conservative hypothesis

Answer 14

complete parent DNA molecule acts as template for new daughter molecule, assembled from new nucleotides and parent molecule is unchanged

Question 15

semi-conservative hypothesis

Answer 15

parent DNA molecule separates into 2 stands which act as templates for new strands, daughter DNAs have half parent DNA and half new

Question 16

Meselson and Stahl 1958 experiment

Answer 16

• grew bacteria e-coli with different isotopes of nitrogen as they knew all bases contain nitrogen
• exposed to N15 for several generations until exposed to lighter N14
• could then distinguish between DNA densities by centrifuging
• after one generation only one band (14/15 hybrid)
• after second two bands (one light 14 and one hybrid)

Question 17

steps of transcription

Answer 17

1. DNA unzips
2. H bonds between bases break
3. mRNA is copy of one side of DNA with code for protein (sense/coding strand) 5’to3’ formed by RNA polymerase
4. mRNA complementary to DNA template 3’to5’ (antisense)
5. DNA too big to leave nuclear pore so mRNA leaves and goes to ribosome for PS

Question 18

formation of mRNA in transcription

Answer 18

1. free nucleotides pair with bases of antisense/template strand when DNA unzips
2. thymine replaced with uracil
3. phosphodiester bonds form between RNA nucleotides due to RNA polymerase
4. transcription stops at end
5. mRNA detaches and leaves nucleus

Question 19

steps of translation

Answer 19

1. mRNA is at ribosome and tRNA with codon enters ribosome
2. tRNA attaches to mRNA and ribosome induces formation of peptide bond which joins the growing chain of AA
3. ribosome moves along mRNA strand so next tRNA can be added
4. tRNA released and recycled

Question 20

steps of protein synthesis

Answer 20

1. mRNA copy of gene made in nucleus
2. leaves through pore
3. attaches to ribosomes on RER
4. moves into RER cisternae + packaged in vesicle
5. vesicle goes to golgi along cytoskeleton
6. vesicle fuses with cis face releasing protein
7. protein leaves through trans face
8. vesicle carries protein to membrane and releases it