nucleic acids 2.1.3

Question 1

what is the structure of a nucleotide ?

Answer 1

a phosphate base connected to a pentose sugar , connected to a nitrogenous base

they all contain elements C,H,O,N,P
they are the monomers that form the basis of the nucleic acids DNA and RNA

Question 2

which pentose sugar is in DNA and RNA ?

Answer 2

DNA - deoxyribose
RNA - ribose

Question 3

what are the four bases ?

Answer 3

purines : larger bases with a double carbon ring
Adenine and guanine
pyrimidines : smaller bases with a single carbon ring
Thymine and cytosine

Question 4

how is a nucleotide formed ?

Answer 4

the sugar and base combine first and a nucleoside forms
then the phosphate group joins nucleotide forms and water with a phosoester bond

Question 5

how do polynucleotides form ?

Answer 5

nucleotides join up between the phosphate group of one nucleotide and the sugar if another via a condensation reaction. this forms a phosodiester bond.
this creates a sugar-phosophate backbone in a 5 prime 3 prime direction

Question 6

how are polynucleotides broken down again ?

Answer 6

hydrolysis

Question 7

what is the structure of DNA ?

Answer 7

composed of two polynucleotide strands in a double helix shape. they join together with hydrogen bonds between the bases in their complementary pairings ( adenine to thymine , and guanine to cysteine ). 3 bonds form between (C+G) 2 bonds form between (A+T). the two strands run antiparallel to each other

Question 8

how is DNA packed into the nucleus ?

Answer 8

it is wrapped around protiens called histones

Question 9

what is the structure of ATP ?

Answer 9

3 phosphate groups connects to a ribose sugar which connects to the base

Question 10

what can be said about the bonds between the phosphate groups in ATP ?

Answer 10

they are unstable and easily broken

Question 11

How are the phosphates removed from ATP ?

Answer 11

hydrolysis

Question 12

what is the equation for the breakdown and formation of ATP ?

Answer 12

ATP –> ADP + Pi
or the reverse for the formation
ADP + Pi –> ATP and this is called photoporation

Question 13

how is ATP suited to the transfer of energy ?

Answer 13

small and soluble - move into and out of cells
releases energy in small quantities - prevents energy waste
unstable phosphate bonds - easily broken
easily regenerated ( ADP->ATP)

Question 14

how do RNA nucleotides differ to DNA nucleotides ?

Answer 14

it has ribose sugar not deoxyribose
uracil instead of thymine
small enough to leave nucleus + travel to ribosomes
after protein synthesis, RNA molecules are degraded in the cytoplasm. phosodiester bonds are hydrolysed and RNA nucleotides are recycled

Question 15

what’s the difference between DNA and RNA ?

Answer 15

DNA :
- double stranded
- pentose sugar is deoxyribose
- contains bases A,T,C,G
- remains in the nucleus
RNA :
- single stranded
- pentose sugar is ribose
- contains bases A,U,C,G
- mRNA can leave the nucleus and travel to ribosomes

Question 16

how does the chromosomes duplicate ?

Answer 16

just before the cell divides the chromosomes become shorter , thicker and more visible
each chromosome duplicates and becomes 2 strands , each called chromatids joined at the centre in a centromere

Question 17

what does the enzyme helicase do ?

Answer 17

separates the two DNA strands by breaking the hydrogen binds between them

Question 18

what is the purpose of single stranded binding proteins ?

Answer 18

to keep the strands apart and stop them from binding again with hydrogen bonds

Question 19

where do the new nucleotide that are added to form the new strands come from ?

Answer 19

free floating DNA nucleotides that have complementary bases

Question 20

what is DNA polymerase role ?

Answer 20

to catalyse the joining of nucleotides with phosodiester bonds

Question 21

in which direction does DNA polymerase add nucleotides ?

Answer 21

5 prime to 3 prime

Question 22

what is the name of the strand that is formed continuously ?

Answer 22

leading strand

Question 23

what is the name of the strand that is formed in a discontinuous way ?

Answer 23

lagging strand

Question 24

what are sections called formed by addition of complimentary bases ?

Answer 24

okazaki fragments

Question 25

which enzyme is required to seal the gap between the okazaki fragments ?

Answer 25

DNA ligase

Question 26

how are errors formed in DNA ?

Answer 26

occur randomly and spontaneously they aren't always harmful and can sometimes be advantageous during replications enzymes proofread the incorrect nucleotides to reduce the rate of mutations

Question 27

what is conservative replication ?

Answer 27

a theory of DNA replication where the whole double helix copies itself meaning that

Question 28

what is the nature of the genetic code ?

Answer 28

universal - in nearly all living organisms the same triplet of DNA bases code for the same amino acid degenerate - each amino acid is coded for by more than 1 dna triplet nonoverlapping

Question 29

what is the difference between RNA and DNA ?

Answer 29

RNA - single stranded ribose sugar uracil not thymine can leave nucleus to the ribosome DNA - double stranded deoxyribose sugar thymine stays in nucleus

Question 30

what are the stage of protein synthesis ?

Answer 30

-transcription of gene in nucleus , mRNA is formed -processing of mRNA -translation of mRNA in a ribosome, polypeptide chain is formed -modification of a protein

Question 31

explain the steps of transcription

Answer 31

1. helicase unzips the strands by breaking hydrogen bonds 2. RNA polymerase moves along the antisense strand in a 5' to 3' direction 3. it forms a complementary mRNA strand by using the antisense strand as a template, by adding free RNA nucleotides and forming phosodiester bonds 4.the mRNA strand separates when it reaches the terminator region and leaves the nucleus, the DNA recoils

Question 32

what is a tRNA ?

Answer 32

made in the nucleus and leave via a nuclear pore and enter the cytoplasm they attach to a specific amino acid they are single stranded RNA polynucleotides that fold into a 3 looped hair pin structure

Question 33

what is the process of translation ?

Answer 33

1. The ribosome attaches to the mRNA strand at a start codon 2. A tRNA molecule, carrying a specific amino acid and with an anticodon that is complementary to the start codon, binds to the mRNA. 3. A second tRNA molecule with an anticodon complementary to the next mRNA codon, and also carrying a specific amino acid, attaches to mRNA. 4. The amino acids carried by the first two tRNA molecules are linked together via a peptide bond using ATP. 5. The first tRNA molecule detaches from mRNA and is free to collect another amino acid for future use. 6. The ribosome moves along mRNA, allowing another tRNA molecule, which carries the next amino acid, to bind to the next codon on mRNA. The process from step 4 to 6 is repeated, which elongates the polypeptide chain. 7. At any point during this process, two tRNA molecules can be attached to the ribosome. 8.The sequence continues until the ribosome reaches a stop codon on mRNA. 9.The completed polypeptide chain detaches from the ribosome

Question 34

what is a gene mutation ?

Answer 34

a change in the bade sequence of a gene which can cause a change in a polypeptide chain. caused by errors that occur during DNA replication mutation rate is low in humans because there are enzymes that check the bases and correct errors mutations are random and spontaneous they can be harmful, beneficial or have no effect

Question 35

explain the steps to DNA purification ?

Answer 35

1. add washing up liquid = breaks down plasma membranes 2. add sodium chloride = breaks hydrogen bonds between DNA and water molecules making DNA less soluble 3. place in a 60 degree water bath for 15 mins = partially denaturing DNA enzymes ( which would otherwise breakdown DNA ) 4. place in an ice bath for 5 mins = to slow down the breakdown of DNA 5. blend for 5 secs = break open the cell walls allowing the release of DNA 6. filter = to obtain filtrate contain proteins and DNA 7. add protease = to hydrolyse the proteins associated with DNA 8. add ice cold ethanol = to precipitate the DNA as it is insoluble in ethanol and the cold inhibits enzyme activity