topic two - nucleic acids - mr hedditch

Question 1

state the two types of nucleic acids?

Answer 1

DNA – deoxyribonucleic acidcontains the pentose sugardeoxyribose

RNA – ribonucleic acidcontains the pentose sugar
ribose

Question 2

what does each DNA nucleotide contain?

Answer 2

a phosphate group
a deoxyribose sugar molecule (pentose – 5C)
one of four nitrogenous bases

Question 3

what are the four nitrogenous bases in DNA?

Answer 3

adenine (A)
thymine (T)
cytosine (C)
guanine (G)

Question 4

what are nucleotides monomers of?

Answer 4

nucleic acids

Question 5

how are the tree subunits (phosphate, deoxyribose, nitrogenous base) joined together?

Answer 5

joined by covalent bonds formed by condensation reactions

Question 6

what different about the RNA to DNA?

Answer 6

RNA has a ribose sugar and instead of thymine its uracil

Question 7

state the similarity between DNA and RNA?

Answer 7

they are both joined by covalent bonds and formed by a condensation reaction

Question 8

are DNA purines or pyrimidines and why?

Answer 8

they are purine bases because they have two carbon-nitrogen rings, joined together

these are

adenine
guanine

Question 9

are RNA purines or pyrimidines and why?

Answer 9

they are pyrimidine bases because they have a single carbon-nitrogen ring (smaller than a purine base)

these are

cytosine
thymine (DNA only) /Uracil (RNA only)

Question 10

draw the simple diagram of a RNA nucleotide with any one of the bases?

Answer 10

check in book or olc

Question 11

draw the simple diagram of a DNA nucleotide with any one of the bases?

Answer 11

check in book or olc

Question 12

define a phosphorylated nucleotide?

Answer 12

a nucleotide with one or more phosphate groups added to it

Question 13

state the two types of phosphorylated nucleotides and how many phosphate groups they contain?

Answer 13

ADP – adenosine diphosphate (two phosphate groups)

ATP – adenosine triphosphate (three phosphate groups)

Question 14

what makes up the base and the sugar of ADP & ATP?

Answer 14

both molecules have the nitrogenous base adenine

and the pentose sugar ribose

Question 15

draw the simple diagram for ADP and ATP?

Answer 15

check in book or on the olc

Question 16

define ATP?

Answer 16

universal energy source meaning it does the same job and production in all living specimens

Question 17

how is ATP produced?

Answer 17

through a series of oxidation reactions that break down food

Question 18

why is ATP continuously hydrolysed?

Answer 18

so ADP can be released and than re-synthesised

Question 19

can ATP be transported from cell to cell and why?

Answer 19

no, it must be used in the cell in which it’s made

Question 20

what is ATP made of?

Answer 20

three phosphate groups and 2 high energy bonds

Question 21

draw the simple diagram of ATP and ADP?

Answer 21

ATP is three phosphate groups

ADP is two phosphate groups

Question 22

how is an inorganic molecule produced?

Answer 22

the hydrolysis of ATP to ADP is catalysed by the enzyme ATPase
this release energy as well as an inorganic molecule

Question 23

what does jointing nucleotides form?

Answer 23

polynucleotides

Question 24

what happens in respiration (ATP)?

Answer 24

ADP is converted back to ATP by adding a phosphate group

Question 25

how is a phosphate bond formed?

Answer 25

a condensation reaction takes place between the phosphate group of one nucleotide and the sugar molecule of a second nucleotide

Question 26

what is base pairing and why does this happen?

Answer 26

A & T And C & G will always pair up because A&T have have 3 hydrogen bonds and C&G have two hydrogen bonds

Question 27

what does the high number of hydrogen bonds do to DNA?

Answer 27

it makes it a very stable structure

Question 28

describe the structure of a double strand?

Answer 28

``` “antiparallel” This refers to the fact that the sugar phosphate backbones run parallel to each other but in opposite directions ```

Question 29

what gives the sugar phosphate backbone?

Answer 29

phosphodiester bonds

Question 30

draw the simple production of phosphorylation?

Answer 30

check with the olc

Question 31

what is the amount of energy released when ATP is hydrolysed to ADP?

Answer 31

releases a large amount of energy (30.6kJ mol-1)

Question 32

what phase does DNA replication occur in?

Answer 32

interphase

Question 33

why is it important for DNA to be copied accurately?

Answer 33

so that the new cells will contain the correct genes to function properly and to produce the correct protein

Question 34

why must chromosomes be copied before mitosis?

Answer 34

so that the new cells contain genetic information

Question 35

state the five stages of DNA replication?

Answer 35

gyrase causes the double helix to unwind hydrogen bonds between bases are broken by helicase to separate the two strands, which can act as templates free nucleotides align next to the exposed bases according to the complementary base-pairing rule hydrogen bonds form between the free nucleotides and nucleotides of the original strands DNA polymerase forms phosphodiester bonds between the phosphate of one nucleotide and the deoxyribose sugar of the next nucleotide, sealing the sugar-phosphate backbone

Question 36

Why is DNA replication described as “semi-conservative”?

Answer 36

this is because the two original “parent” strands act as templates for the formation of new strands. each replicated molecule contains one old strand and one new strand

Question 37

describe what the enzyme 'gyrase' does in DNA replication?

Answer 37

unwinds the double helix

Question 38

describe what the enzyme 'helicase' does in DNA replication?

Answer 38

breaks the hydrogen bonds between the two parental strands of DNA, at a number of different points called replication forks

Question 39

describe what the enzyme 'polymerase' does in DNA replication?

Answer 39

joins the nucleotides in the new strand together (makes phosphodiester bonds) to form a sugar-phosphate backbone

Question 40

is DNA replication accurate and why?

Answer 40

DNA replication is very accurate – this is essential for | genes to be conserved, and is ensured through the action of proof-reading enzymes

Question 41

name the three types of evidence for semi-conservative replication and what they are?

Answer 41

semi-conservative – the DNA molecule splits and each strand is replicated. Each of the two new molecules contains one strand of original material and one strand of new material conservative - parental DNA remains intact and a separate daughter copy is built out of new molecules. Of the two molecules present, one is the original and one is entirely new material dispersive – the parental DNA is broken down and the nucleotides replicated before being randomly dispersed throughout the new molecules. The new molecules contain both new and original material but not necessarily in equal amounts

Question 42

what does exonuclease do in DNA replication?

Answer 42

it removes all the RNA which is then filled with DNA

Question 43

define gene?

Answer 43

a gene is a length of DNA that codes for a polypeptide

Question 44

why does each gene contain a sequence of DNA triplets?

Answer 44

it determines the amino acid sequence (or primary structure) of a protein

Question 45

why must a copy of each gene be transcribed into a length of mRNA?

Answer 45

the instructions contained in the genes cannot pass out of the nucleus

Question 46

define a codons?

Answer 46

a codon is a set of three adjacent nucleotides (bases) on a strand of mRNA each codon specifies for one particular amino acid

Question 47

what does the order of the codons along the mRNA strand determines?

Answer 47

determines the | sequence of the amino acids in the polypeptide

Question 48

why is the genetic code described as universal?

Answer 48

because the same DNA bases (or mRNA codons) | code for the same amino acids in almost all organisms

Question 49

why are there three nucleotides in a codon?

Answer 49

There are four bases in DNA: – adenine, guanine, thymine and cytosine clearly, it is not possible to have one base coding for each of the 20 different amino acids similarly, using two bases would be insufficient – would only code for 16 different amino acids using three bases gives 64 possible unique combinations - more than enough! the triplet code has spare coding capacity – i.e. there are more unique codons (64) than there are amino acids to be coded for (20) therefore it is possible for several codes to be used to specify the same amino acid – e.g. phenylalanine can be coded for by AAA and AAG – e.g. leucine can be coded for by AAT, AAC, GAA, GAG, GAT and GAC because of this, the code is described as degenerate

Question 50

define degenerate?

Answer 50

degenerate refers to a code in which several code words have the same meaning. The genetic code is degenerate because there are many instances in which different codons specify the same amino acid

Question 51

what are the three forms of RNA?

Answer 51

mRNA messenger RNA a "copy" of the DNA base sequence of a gene complementary to one strand of the DNA (template strand). The coding sequence of the mRNA determines the amino acid sequence in the polypeptide that is produced single-stranded, with uracil in place of thymine rRNA ribosomal RNA ribosomes are made of rRNA and protein (two sub-units) tRNA transfer RNA small molecule ~ 80 nucleotides hydrogen bonds make a stable clover-leaf shaped structure 20 types – one for each of the different amino acids delivers (transfers) amino acids to growing polypeptide chains in the ribosome in the specific order directed by mRNA

Question 52

state the processes of transcription?

Answer 52

the DNA double helix “unzips” as hydrogen bonds between complementary bases break (due to helicase) and the two polynucleotide strands separate one DNA strand acts as a template. Free RNA nucleotides complementary base-pair to the exposed bases on this strand by forming hydrogen bonds. mRNA contains U in place of T RNA polymerase forms phosphodiester bonds between the sugar and phosphate parts of the RNA nucleotides the mRNA detaches from the template strand of the DNA the two DNA strands join together by complementary base pairing (hydrogen bonds reform) and the DNA molecule winds back up into a helix

Question 53

ways transcription is similar to DNA replication?

Answer 53

the DNA molecule unwinds and unzips helicase is involved in breaking hydrogen bonds exposed bases act as a template for the formation of a new polynucleotide strand complementary base pairing ensures that the message is transcribed accurately the free nucleotides joining the new polypeptide chain are joined together by phosphodiester bonds

Question 54

ways transcription is different from DNA replication?

Answer 54

only one DNA strand, the template strand, is copied (in DNA replication both strands act as templates) RNA polymerase joins the sugar-phosphate backbone (not DNA polymerase) mRNA is single-stranded and a relatively short molecule with uracil in place of thymine  Only a single gene is transcribed, whereas in DNA replication the whole chromosome is copied

Question 55

what happens in the move from transcription to translation?

Answer 55

mRNA moves out through a nuclear pore and attaches to a | ribosome

Question 56

what does tRNA transport?

Answer 56

transports amino acids to the ribosome for incorporation into a polypeptide chain

Question 57

what do hydrogen bonds between the complementary bases do in tRNA?

Answer 57

stabilise the clover-leaf shape

Question 58

what two things does tRNA have?

Answer 58

an anticodon that is complementary to a codon on the mRNA three unpaired bases to which a specific amino acid can be attached (called the attachment site)

Question 59

state what takes place in translation?

Answer 59

during translation, mRNA enters the groove between the small and large ribosomal subunits the ribosome is large enough for two codons to fit side by side the very first codon is always the start codon AUG (codes for methionine) the anticodon of a tRNA molecule carrying methionine hydrogen bonds to the first codon to start translation a second tRNA molecule, carrying the second amino acid coded for, hydrogen bonds to the second codon a peptide bond is formed between the two amino acids through a condensation reaction the ribosome moves three bases (one codon) along the mRNA so that another codon is exposed a third tRNA brings another amino acid which is added to the dipeptide and so the process continues until a termination or stop codon (UAA, UAG or UGA) is reached there is no tRNA for stop codons, so the polypeptide chain and mRNA are released from the ribosome translation takes place in the cytoplasm at the ribosomes

Question 60

what are the two subunits in translation?

Answer 60

a large subunit and a small subunit, bound together with the aid of magnesium ions – with a groove between them in which the mRNA fits

Question 61

study the transcription/translation grid sheet?

Answer 61

in biology folder