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biology year 1 > enzymes and nucleic acids > Flashcards

enzymes and nucleic acids Flashcards

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1
Q

describe the structure of enzymes

A

-tertiary proteins with globular shape
-has a pocket or cleft area which has a specific 3D shape called an active site where reactions take place

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2
Q

function of enzymes

A

-act as biological catalysts
-provide an alternate pathway during a reaction
-hydrolyse polymers into monomers in digestion

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3
Q

define biological catalyst

A

proteins that speed up metabolic reactions without being used up

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4
Q

how do enzymes lower activation energy?

A

by providing an alternate pathway during a reaction

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5
Q

what is the importance of the enzyme catalase?

A

-hydrolyses hydrogen peroxide into water + oxygen
-H202 is a toxic by-product of metabolism so must be removed
-catabolic

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6
Q

whats the importance of the enzyme RUBISCO?

A

-RuBP +CO2 into glycerate + phosphate
- fixes CO2 from atmosphere in photosynthesis
-anabolic

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7
Q

whats the importance of the enzyme ATPsynthase?

A

ADP +Pi into ATP
-energy requiring process
-active transport
-anabolic

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8
Q

whats the of the enzyme glycogen synthetase?

A

-converts glucose to a storage compound -glycogen (polysaccharide)
-anabolic
condensation

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9
Q

define activation energy

A

the extra energy that is required to enable a reaction to occur

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10
Q

where is the activation energy usually supplied through?

A

heat in a loboratory reaction

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11
Q

whats the importance of a model?

A

it provides simplified visual representations to explain how a process may work

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12
Q

describe the lock and key model of enzyme action

A

-specific active site is complementary to the substrate molecule so able to bind
-bonds broken
-2 products are formed

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13
Q

describe the induced fit hypothesis of enzyme action

A

-active site not fully complementary
-strain on bonds lowers activation energy
-the active site becomes complementary to the substrate
-an enzyme-substrate complex forms
-substrate no longer fits active site so products are released

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14
Q

what biochemical food test would determine if an enzyme was present?

A

-biuret solution (NaOH + CuSO4)
-blue to lilac

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15
Q

what factors may affect the rate of reaction of enzyme?

A

-pH
-temperature=Ke
-substrate concentration
-enzyme concentration

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16
Q

why will an enzyme only bind to one substrate molecule?

A

active site is only complementary to one type of substrate molecule

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17
Q

what is a limiting factor?

A

factors that effect maximum rate of reaction being achieved

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18
Q

explain how a very high temp can stop an enzyme from working?

A

-bonds will break
-active site denatures
-can no longer bind, no longer complementary to the substrate
-no enzyme-substrate complexes can form

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19
Q

explain how extreme pH can affect the overall shape of the enzyme

A

-hydrogen ions can interfere with R group interactions between amino acids as H+ will cluster around negatively charged R groups and disrupt the hydrogen and ionic bonds which maintain the tertiary structure of a protein and shape of active site

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20
Q

what is meant by the saturation point in an enzyme controlled reaction?

A

when all enzymes active sites are occupied

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21
Q

what is the limiting factor when increasing the substrate concentration?

A

enzyme concentration

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22
Q

explain the effect of temperature on enzyme activity

A

-as temp increases, the molecules have more kE
-more successful collisions between substrates and the enzymes active sites
-so more enzyme-substrate complexes
-so rate of reaction happens faster

-when the temp goes beyond optimum, H bonds break
-enzyme denatures + tertiary 3D structure of active site changes
-active site changes shape so more difficult to become complementary to the substrate
-so fewer to no enzyme-substrate complexes can form
-so rate of reaction slows down and stops

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23
Q

why are rate of reactions very slow at low temps?

A

enzymes and substrate molecules have little kinetic energy
and few enzyme-substrate successful collisions taking place

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24
Q

explain the effect of pH on enzyme activity?

A

-as the pH moves away from optimum, rate decreases
-because changes in pH changes charges on the R groups of the amino acids
-therefore this changes the ionic and hydrogen bonding
-therefore 3D tertiary structure of enzymes changes
-so active site denatures, no longer easy for active site to become complementary
-so fewer enzyme-substrate complexes can form
-so rate decreases then stops

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25
Q

what are the 2 main ways of measuring the rate of a reaction?

A

-start the reaction, then measure either the concentrations of product formed or substrate used up after a fixed time intervals

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26
Q

define initial rate

A

the rate of reaction is at its highest at the first few seconds beginning of the reaction when the conc of substrate molecule is highest and therefore more enzyme-substrate collisions so more ESCs formed

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27
Q

define v-max

A

point at which the reaction is fastest as all the enzyme active sites are occupied no more enzyme substrate complexes can be formed

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28
Q

formula for rate

A

1/time

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29
Q

explain the effect of increasing concentration of substrate on the rate of an enzyme catalysed reaction?

A

-if conc of enzymes remains constant and conc of substrate increases the number of collisions will increase
-more ESCs
-rate increases
-saturation point will be reached
-conc of enzymes active site limiting factor

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30
Q

explain the effect of increasing enzyme concentration on the rate of an enzyme catalysed reaction?

A

-as the enzyme conc increases there are more active sites available
-greater chance that substrates will collide with the active sites
-more ESCs can form
-initial rate increases
-conc of substrate limits any further increase

31
Q

what are the 2 types of inhibitors?

A

non-competetive
competitive

32
Q

describe how competitors work

A

-similar shape to the substrate molecule
-complementary shape to the active site of the enzyme
-they enter active site and bind forming an enzyme-inhibitor complex
-prevent normal substrate from entering by blocking active site
-number of ESCs that can form are reduced and rate of reaction falls

33
Q

describe how non-competitors inhibitors work?

A

-dont compete with substrate for active site
-attatch away at allosteric site and distort the 3D tertiary shape of the enzyme- change in active site shape
-substrate no longer fits active site
-ESC cannot form, rate of reaction decrease
-inhibitor may be completely diff shape to substrate

34
Q

what are reversible inhibitors?

A

do not permanently bind with the active site or away from the active site so not permament

35
Q

what are permament inhibitors?

A

permanently bind to the active site or away from the active site

36
Q

what are the 2 types of nucelic acids?

A

DNA- deoxyribonucleic acid
RNA ribonucleic acid

37
Q

what do nucleic acids form?

A

monomers called nucleotides

38
Q

what are the components of nucleic acids?

A
  1. phosphate group
  2. pentose 5c carbon sugar
    dna- deoxyribose
    rna- ribose
  3. nitrogen containing bases
    DNA- adenine, Thymine, cytosine and guanine
    RNA- adenine, uracil, cytosine and guanine
39
Q

define the complementary base pairing rule

A

-adenine is able to pair through hydrogen bonds with thymine (or uracil in RNA)
-guanine is able to pair through hydrogen bonds with cytosine
-pyrimidines on one strand of DNA form H bonds with purines to hold strands together

40
Q

how are nucleic acids formed?

A

-nucleotides link together to form polynucleotides
-condensation reactions
-covalent phosphodiester bond forms between C3 of one nucleotide and the phosphate of adjecent nucleotides
-forms sugar-phosphate backbone

41
Q

what are purines complementary to?

A

pyrimidines

42
Q

what are purines?

A

2 carbon nitrogen ring bases
-adenine
-guanine
(Pure As Gold)

43
Q

what are pyrimidines?

A

1 carbon nitrogen ring bases
-cytosine
-uracil
-thyine
(pyramids CUT)

44
Q

describe and explain the structures and functions of DNA

A

S=hydrogen bonds which join the 2 strands are weak bonds
F= allows easy separation of strands during DNA replication and protein synthesis
S= two strands
F= both can act as a template in DNA replication
S=many hydrogen bonds between base pairs
F= strength, stabalises structure
S=complementary base pairing
F= accurate DNA replication and transcription and allows a specfic sequence of bases to code for a specific primary structures of protein

45
Q

structure of RNA

A

-short single stranded polynucleotide chain
-pentose sugar is ribose
-organic bases are adenine, uracil, guanine and cytosine

46
Q

what are the 3 types of RNA?

A

-mRNA=messenger RNA - transfers the genetic information from DNA to the ribosome
-rRNA=ribosomal RNA - together with proteins makes up the ribosome
-tRNA= Transfer RNA- transfers specific amino acids to the ribosome for protein synthesis

47
Q

describe the process of semi conservative replication

A

1) double helix is untwisted
2)enzyme DNA helicase breaks the hydrogen bonds exposing nucleotide bases
3)both strands act as a template
4) free complementary DNA nucleotide bases hydrogen bond to exposed bases
5)complementary base pairing rule
6)phosphodiester bonds are formed to join sugar phosphate backbone by DNA polymerase
7) one conserved old strand and one new strand

48
Q

what is the active site of DNA polymerase compemenyary to? whats the importance?

A

the 3’ end of deoxyribose.
means the enzyme can only add new nucleotides to the new strand at the 3’ end
because the strands are antiparallel DNA polymerase working on one of the template strands works in the opposite direction to the DNA polymease working on the oher strand

49
Q

who provided evidence for semi conservative replication?

A

messelson and stahl

50
Q

what did messelson and stahk do?

A

they grew E coli bacteria for many generations in a medium of 15N-heavy nitrohen

51
Q

why was the DNA in the bacteria grown on 15N denser?

A

because the bases contained N15

52
Q

describe the steps of the experiment of semi conservtive replication

A

-E coli grown in 15N
DNA us centrifuged in CsCk = heavy DNA band
-bacteria transfered to 14N and griw for one generation
-DNA is centrifuged in CsCl = hybrid DNA
-grown for second generation in 14N
-DNA centrifuged in CsCl = 2 bands onr hybrid one light

53
Q

what modes were disproved by messelson and stahl experiment?

A

-conservative model
-dispersive model

54
Q

describe the conservative model

A

each replication results in one DNA molecule that consists of both original strands of DNA, and one DNA molecule that consists of 2 completely ne strands of DNA

55
Q

describe the dispersive model

A

each replication results in 2 DNA molecules that are combinations of original and new DNA

56
Q

what does ATP stand for?

A

adenosine triphosphate

57
Q

describe the structure of ATP

A

-phosphorylated nucleotides
-formed from a nitrogen containing orgaic base = adenine
-a 5 carbon ribose sugar
-and a chain of 3 phosphate groups

58
Q

whats the advantage of the phosphate bonds in ATP being unstable?

A

makes ATP a good energy source
immediate source as cell cant get energy directly from glucose

59
Q

whats the role of ATP synthase?

A

catalyses the energy needed by phosphates to form a condensation reaction

60
Q

whats the role of ATP hydrolase?

A

breaks phosphate bonds releasing small packets of energy in a hydrolysis reaction

61
Q

what is ATP used for?

A

-phosphorylation of compounds= makes more reactive
-active transport = change shape of carrier proteins in plasma membranes- moving molecules agaisnt a conc gradient
-metabolic processes
-exocytosis
-movement = muscle contraction

62
Q

give 2 examples of phosphorylation of compounds

A

-glucose to glucose phosphate in glycolysis
-photophosphorylation in plant cells during photosynthesis

63
Q

give 2 examples of ATPs use in metabolic processes

A

-synthesising glycogen from glucose
-polypeptides from amino acids

64
Q

whats the formula for ATP synthesis?

A

ADP + Pi = (condensation) ATP + H2O

65
Q

How might a change in the primary structure result in a non-functional enzyme?

A

A change in amino acid sequence results in different R groups

Results in a change in hydrogen / ionic / disulfide bonds

Which results in a change in the tertiary structure

Which changes the shape of the active site;

Substrate is not complementary to the active site so no enzyme-substrate complexes form.

66
Q

Describe the INDUCED FIT model

A

Enzymes have an active site with a specific shape.

Before the reaction the active site is not complementary to the substrate.

The active site changes shape and becomes complementary as substrate binds

An enzyme- substrate complex is formed

This stresses and bends the bonds in the substrate which allows the reaction to occur

67
Q

How do enzymes affect the activation energy?

A

Enzymes lower the activation energy allowing chemical reactions to take place at lower temperatures than they would otherwise occur (e.g. body temperature).

68
Q

What is the active site of an enzyme and what is it’s function?

A

It is the functional part of the enzyme that binds to the substrate by becoming complementary to the shape of the substrate. This allows the formation of an Enzyme-Substrate Complex (E-S complex).

69
Q

How will a high substrate concentration affect the number of collisions? with non-comp and comp inhibitor?

A

non-comp= At high substrate concentrations there are less enzyme-substrate collisions

comp= At high substrate concentrations there are more enzyme-substrate collisions

70
Q

explain function of following structures on DNA

Sugar-phosphate backbone

Helix/Coiling

Large Molecule

Sequence of bases

Double helix with many hydrogen bonds

Double stranded/Two strands

Double helix

Hydrogen bonds between the bases are weak and easily broken

Complementary base pairings

A

Gives strength

Gives it a compact shape

Stores lots of information

Allows information to be stored/codes for amino acids

Makes the DNA molecule stable

BOTH strands can act as templates during semi-conservative replication

Prevents the code being corrupted

Allows the strands to be separated for replication and also for protein synthesis

Allows accurate replication

71
Q

What is meant by specific base pairing?

A

Each base is complementary to one other base – this is the one that it binds to.

Guanine and cytosine are complementary to each other and therefore ONLY bind to each other

Adenine and thymine are complementary to each other and therefore ONLY bind to each other

72
Q

Describe the differences between DNA and RNA (5 marks)

A

DNA has A,T,C,G bases whereas RNA has A,U,C,G

DNA has a deoxyribose sugar whereas RNA has a ribose sugar

DNA is double stranded wheras RNA is single stranded

DNA is a large polymer RNA is a short polymer

DNA holds genetic information in the nucleus whereas RNA transports genetic information to the ribosome

73
Q

Describe the differences between DNA in prokaryotes and Eukaryotes

A

DNA in eukaryotes is coiled up around proteins called HISTONES whereas the DNA in prokaryotes is not

DNA in eukaryotes is linear whereas DNA in prokaryotes is circular

DNA in eukaryotes is found in a nucleus, whereas DNA in prokaryotes is in the cytoplasm

74
Q

What is the link between DNA bases, amino acids and a protein?

A

A sequence of bases codes for a sequence amino acids to form a polypeptide chain which can fold into a protein.

biology year 1 (8 decks)

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