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A-LEVEL BIOLOGY > DNA > Flashcards

DNA Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

why does DNA replication occur before cell division?

A

so each new cell has a copy of DNA

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2
Q

describe DNA replication steps

A

1) DNA helicase unwinds/unwraps DNA double helix
2) exposed bases bind to free floating nucleotides in the nucleoplasm
3) DNA polymerase binds the complementary nucleotides to unpaired bases which reproduces the original DNA molecule exactly
4) replication is semi-conservative (1 old + 1 new strand)

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3
Q

what’s DNA helicase?

A

opens up double strand

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4
Q

what’s DNA polymerase?

A

enzyme that makes DNA polymers

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5
Q

where does DNA replication occur?

A

replication fork

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6
Q

what is RNA primer made of?

A

RNA primase

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7
Q

whose experiment proved semi-conservative replication with data?

A

meselson and stahl

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8
Q

define DNA replication

A

copying of DNA molecules to produce more DNA

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9
Q

describe meselson and stahl’s experiment

A
  • grew bacterium (E. coli) in the presence of radioactive 15N until a culture was obtained
  • the DNA was labelled 15N
  • subculture of the labelled bacterium was transferred for growth in the presence of normal 14N
  • the generation time of E. coli is known so it was possible to take samples of this growing subculture after each gen.
  • each sample’s DNA was extracted + isolated DNA was centrifuged in a caesium chloride sol. at 40,000 G for 20 hrs -> made DNA sediment out
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10
Q

describe meselson and stahl’s experiment THEORY

A
  • the heavier the DNA, the further down it moved in the centrifuge tubes
  • (15N DNA is heavier than 14N, so it moved to the lowest position)
  • after 1 gen. all DNA moved to intermediate position -> showed presence of mixed 14 + 15N -> DNA in the gen. had 1 strand of parent molecule and 1 new strand
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11
Q

why did meselson and stahl’s experiment disprove the conservative hypothesis?

A

if it was true, 2 DNA masses would’ve been visible -> 1 heavy, 1 light (not intermediate)
in the 2nd gen. half of the DNA was intermediate and the other half was light

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12
Q

describe DNA structure

A 
double stranded helix molecule
2 polynucleotide chains coiled
polymer with repeating monomers 
nucleotides
4 bases -> ATCG
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13
Q

what bonds the sugar and phosphate in a nucleotide

A

phosphodiester bonds

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14
Q

what bonds bases together

A

H-bonds

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15
Q

how many hydrogen bonds between base pairs

A

AT -> 2

CG -> 3

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16
Q

state an easter linkage

A

O=C-O

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17
Q

define gene

A

section of DNA

sequence of 3 bases that code for a specific AA for a specific protein

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18
Q

define and give examples of purine bases

A

2 rings
A
G

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19
Q

define pyrimidine bases and give examples

A

1 ring
T
U
C

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20
Q

what can phosphoric acid do?

A

substance that can libertine

H-ions

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21
Q

describe RNA structure

A 
pentose sugar
single stranded
short -> (100-1000 nucleotides long)
ribose 
CG
AU
22
Q

how are nucleotides joined

A

condensation reactions

23
Q

how are the 2 strands in DNA held together

A

H-bonds between bases

24
Q

DNA replication steps

A
  • before cell division so each new cell has a copy of DNA
  • DNA helicase unwinds DNA double helix and it opens up at replication fork
  • exposes bases bind to free floating nucleotides in nucleoplasm
  • DNA polymerase bonds complementary nucleotides to unpaired bases which reproduces original molecule exactly
  • replication is semiconservative (1 old 1 new strand)
  • SEE IMAGES*
25
Q

describe transcription

A
  • in nucleus
  • DNA used as template to make mRNA with RNA polymerase
  • initiation -> DNA helix unwinds
  • elongation -> RNA polymerase slides along template DNA strand, complimentary base pairing
  • nucleotides liked ro 3’ end of growing RNA molecule
  • termination -> RNA polymerase reaches terminator portion of gene, RNA transcript = complete
  • mRNA + RNA polymerase + DNA strand dissociate from e/o
26
Q

describe translation

A
  • mRNA exits nuclear pore into cytoplasm
  • mRNA binds to small ribosomal sub-unit at start codon
  • AA’s brought to ribosome by tRNA
  • complimentary base paring w/ mRNA codons + tRNA anticodons
  • charged tRNA binds to A site -> peptide bond forms between AA’s at A + P site
  • whole complex shifts 1 down to the right
  • uncharged tRNA exits at E site
  • A site accepts next tRNA ->continues until stop codon
  • release factor binds to A site at stop codon
  • polypeptide released from tRNA at P site
  • whole complex dissociates
27
Q

what determines the type of AA?

A

anticodon sequence of tRNA

28
Q

define anticodon

A

sequence of 3 bases on tRNA that complimentary base pair with mRNA codons and fit with each other

29
Q

how are mRNA + tRNA different?

A

mRNA -> 5’ - 3’ , length can change

tRNA -> fixed length

30
Q

which codons dont code for AA’s?

A

stop/start codons

31
Q

define temp.

A

measure of KE of particles of a region

32
Q

define heat

A

measure of total energy within

sum of KE + pot. energy

33
Q

describe entry of substrate to active site

A

forces of attraction -> push + pull
conformation change -> enzyme clamps down around substrate forms induced fit
after reaction, active site returns to original shape

34
Q

state an amine group

A

-NH2

35
Q

state a carboxylic group

A

-COOH

O=C-OH

36
Q

how many diff. AA’s are there in normal proteins

A

20

37
Q

how are peptide bonds formed?

A

condensation reactioms

38
Q

state peptide bond linkage

A

O=C-N-H

SEE IMAGE

39
Q

define catabolic reaction

A

when substances are broken down

40
Q

describe protein primary structure

A

simplest level
*AA seq. of protein in polypeptide chain
peptide bonds link AA’s
each chain has own set of AA’s assembled in particular order determined by DNA of coding gene

41
Q

whats haemoglobin made of?

A

polypeptide chains

42
Q

describe protein tertiary structure

A
  • overall 3D structure due to interactions between R -groups of AA’s that make up proteins
  • H-bonds contribute to structure
  • hydrophobic interactions -> AA’s + non-polar
  • hydrophobic *R groups cluster inside protein
  • leaves hydrophylic AA’s outside to interact with surrounding water molecules
  • fibrous proteins
43
Q

define disulfide bonds?

whats their role?

A

covalent linkages between sulfur containing side chains

keep parts of a polypeptide attached to each other

44
Q

describe protein secondary structure

A

3D organisation of main chain atoms of a protein
(the atoms that all amino acids in a protein have in common)
folded structures that form within polypeptides due to interactions between atoms of the *backbone
parts of polypeptide chain take up certain shape after formation at ribosome -> fold/twist
e.g. a-helix coils/b-helix zig-zag sheets held in shape by H-bonds

45
Q

describe protein quaternary structure

A

some proteins made of many polypeptide chains twist -> subunits that come together
e.g. haemoglobin has 4 sub units

46
Q

how are polypeptides and proteins formed

A

AA monomers linked by peptide bonds by condensation reactions

47
Q

globular proteins

A 
round/spherical 
functional
irregular AA seq.
more sensitive to change (pH/temp)
normally water soluble
48
Q

fibrous proteins

A

polypeptides form long narrow chains parallel to e/o
chains linked by disulphide cross bridges -> stable and strong structure
repetitive AA seq.
less sensitive to change (pH/temp)
normally water INsoluble

49
Q

define enzyme

A

biological catalysts that reduce E.act

50
Q

why are globular proteins soluble in water?

A
  • hydrophobic groups point into centre of molecule away from water
  • only hydrophilic groups are exposed outside the molecule so globular proteins are soluble
51
Q

e.g. of globular proteins

A 
HAVE ROLE ON METABOLIC REACTS.
enzymes - catalyse metabolic reactions
haemoglobin - binds to oxygen to transport it around body
insulin
immunoglobulin
52
Q

e.g. of fibrous proteins

A 
GIVE STRUCTURE
keratin - skin/nails
collagen - bone/cartilage/tendons/ligaments for tensile strength
myosin
fibrin
actin
elastin

A-LEVEL BIOLOGY (8 decks)

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