2.1.3 nucleotides and nucleic acids

Question 1

what is a nucleotide made from

Answer 1

a nitrogenous base
a pentose sugar
a phosphate group

Question 2

what are nucleotides

Answer 2

the monomers of DNA and RNA

Question 3

what bases can be found in DNA

Answer 3

adenine, thymine, cytosine, guanine

Question 4

what pentose sugar is in DNA

Answer 4

deoxyribose

Question 5

what is a purine base

Answer 5

contains 2 carbon nitrogen rings joined together

Question 6

what bases are purines

Answer 6

adenine and guanine

Question 7

what is a pyramidal base

Answer 7

only contains 1 carbon nitrogen ring so they are smaller

Question 8

what bases are pyramidal

Answer 8

thymine and cytosine

Question 9

what is the pentose sugar in RNA

Answer 9

ribose

Question 10

what base is different in RNA

Answer 10

thymine is uracil instead

Question 11

how is energy released from ATP

Answer 11

the phosphate bond stores energy that is released when ATP is broken down into ADP and Pi

Question 12

what does ATP and ADP stand for

Answer 12

ATP - adenine triphosphate
ADP - adenine diphosphate

Question 13

what are the bonds between nucleotides

Answer 13

phosphodiester bonds

Question 14

what is the chain of sugar and phosphates called

Answer 14

the sugar-phosphate backbone

Question 15

what is the structure of DNA

Answer 15

a double stranded helix

Question 16

how are the two DNA strands joined together

Answer 16

hydrogen bonds between complementary bases (complementary base pairs)

Question 17

how many hydrogen bonds between A and T

Answer 17

2

Question 18

how many hydrogen bonds between C and G

Answer 18

3

Question 19

how is the helix shape formed

Answer 19

antiparallel strands twist the DNA

Question 20

how do we purify DNA

Answer 20

break up cells in sample
add detergent (break down cell membranes), salt (binds to DNA and clumps it together) and distilled water to the sample
heat in a water bath at 60 degrees for 15 mins to stop enzymes working
then add to ice bath to cool then filter
add protease to break down proteins and RNAase to break down RNA
drop ethanol down the side forming a layer on top, DNA forms a white precipitate

Question 21

what is semi conservative replication

Answer 21

half the strand in each copy are from the original piece of DNA

Question 22

how does DNA copy itself

Answer 22

DNA helicase breaks hydrogen bonds between strands
each original strand acts as a template for a new strand. free floating nucleotides join to exposed bases by complementary base pairing
nucleotides of new strand are joined by DNA polymerase to make phosphodiester bonds between nucleotides and hydrogen bonds form between strands

Question 23

what is a gene

Answer 23

a sequence of DNA nucleotides that codes for the sequence of amino acids in a polypeptide

Question 24

how many bases codes for a single amino acid

Answer 24

3 it is called a triplet

Question 25

what is mRNA

Answer 25

messenger RNA it is made in the nucleus it carries the genetic code from DNA in the nucleus to the cytoplasm for translation

Question 26

what is tRNA

Answer 26

transfer RNA found in the cytoplasm it has an amino acid binding site at one end of the sequence of 3 base pairs at the other end called an anticodon

Question 27

what is rRNA

Answer 27

ribosomal RNA forms the two subunits in a ribosome and catalyses the formation if peptide bonds between amino acids

Question 28

why is the genetic code said to be non overlapping

Answer 28

each base triplet is read in sequence separate from the triplet before and after it. base triplets do not share bases

Question 29

why is the genetic code said to be degenerate

Answer 29

there are more possible combinations of triplets than there are amino acids this means that some amino acids are coded for by multiple codons. there are also start and stop codons at the ends of the codons

Question 30

why is the genetic code said to be universal

Answer 30

the same specific codons code for the same amino acids in all living things

Question 31

what is the first stage of protein synthesis

Answer 31

transcription

Question 32

what is the purpose in transcription

Answer 32

an mRNA copy of a gene is made in the nucleus

Question 33

what are the steps of transcription

Answer 33

RNA polymerase breaks the hydrogen bonds separating the strands. one of the strands and the DNA molecule is used as a template the RNA polymerase lines up free RNA nucleotides alongside the template using complementary base pairing (U is used instead of T) RNA nucleotides bond to make an mRNA molecule hydrogen bonds reform between DNA strands

Question 34

what is the second stage of protein synthesis

Answer 34

translation

Question 35

what is the purpose in translation

Answer 35

amino acids are joined together to make a polypeptide

Question 36

what are the steps of transcription

Answer 36

mRNA attaches to a ribosome tRNA carries amino acids to ribosome a tRNA molecule with a complementary anticodon to the start codon and attaches itself by complementary base pairing a peptide bond forms between each amino acid and tRNA moves away. this continues until stop codon polypeptide moves away from ribosome when done.