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SNAB Biology Edexcel > Topic 2 > Flashcards

Topic 2 Flashcards

1
Q

in genetic screening, why do carriers sometimes show a false positive

A

the recessive allele may be detected

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2
Q

what does implantation diagnosis consist of

A

embryos are created through IVF are tested to see if they carry faulty allele. Only the healthy embryos will be implanted
however the process is expensive and unreliable

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3
Q

define allele

A

a version of a gene

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4
Q

define a recessive allele

A

an allee which isn’t expressed when a dominant allele is present

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5
Q

define dominant allele

A

an allele is always expressed

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6
Q

define incomplete dominance

A

neither allele is dominant over the other and the resultant phenotype is a mix

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7
Q

what symptoms can cystic fibrosis present in gas exchange

A

mucus can block bronchioles which leads to less O2 to the alveoli so smaller concentration gradients
thin layer of mucus can make it difficult for O2 and CO2 to diffuse

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8
Q

what symptoms can cystic fibrosis present in reproduction

A

in men - sperm duct blocked with mucus so sperm can’t leave the testes
in women - mucus blocks the cervix so sperm cannot reach the egg

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9
Q

what symptoms can CF present in digestion

A

blocks the pancreatic duct so digestive enzymes cannot reach the digestive system so food isn’t properly digestive and nutrients aren’t absorbed so there is difficulty gaining weight
enzymes trapped in the pancreas cause fibrosed cysts and damage insulin producing cells which can also lead to diabetes

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10
Q

what does amniocentesis consist of

A

a syringe with a needle is inserted into the amniotic sac and fluid is extracted and foetal cells are then separated. This is cultured for 2-3 weeks
DNA is karyotyped, biochemical tests are also carried out on both the fluid and cells
this is when the foetus is 14-16 weeks

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11
Q

what does chorionic villus sampling consist of

A

a syringe is inserted in the vagina to take a sample of embryonic tissue from the placenta (the chorionic villus).
DNA is karyotyped when the fetus is 8-10 weeks old

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11
Q

why do people with CF have sticky mucus

A

the CFTR channel protein is non-functional therefore the Na+ channel (ENac) is always open so Na+ ions move into the cell and to the tissue fluid on the basal membrane
this causes the Cl- to move down the concentration gradient, water goes out from the mucus and into the cell and tissue fluid

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11
Q

what are the factors that one must consider in relation to prenatal screening

A

risk of miscarriage, potential abortion, religious beliefs of right to life, cost of healthcare, risks/consequences of false positives/negatives

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12
Q

what is meant by monohybrid inheritance

A

inheritance of 1 characteristic

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13
Q

when can mutations occur

A

DNA replication, transcription and translation

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14
Q

how do bodies decrease the viscosity of mucus on the apical membrane

A

Cl- is pumped into the cell across basal membrane
Cl- diffuses through open CFTR channels to outside apical membrane
Na+ diffuses down electrical gradient in mucus
Elevated salt concentration in the mucus draws water out of the cell and into the mucus via osmosis

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15
Q

what did Meselon and Stahl’s experiment consist of

A
  1. E coli bacteria cultured in 15-N containing medium
  2. transferred into a 14-N containing medium
  3. DNA extracted after each generation and centrifuged into BaCl solution
    the heavier the DNA was, the deeper it sank in the test tube
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16
Q

how did Meselon and Stahl’s experiment disproved the other theories

A
  1. In a conservative model, super heavy DNA would be expected with a newly lighter DNA as generations passed - 1 of each
  2. In dispersive, only 1 layer of equally dense DNA would be seen getting lighter and lighter - a mix of heavy and light
  3. Results showed intermediate strands of 1/2 heavy and 1/2 light after 1 generation which disproved conservative
    After 2 generations, 2 layers were shown, 1 intermediate and 1 light which disproved fragmentary
    semi conservative was 1 strand of intermediate and 1 strand of light in a double helix
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17
Q

why isn’t heat used to accelerate reactions in organisms rather than enzymes

A

heat would damage cell tissues

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18
Q

how do enzyme concentration affect the reaction rates

A

as the enzyme concentration increases, the rate increases as there is a higher chance of successful collisions therefore more enzyme-substrate complexes formed per unit of time so more products are released

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19
Q

in experiments how could
temperature be controlled
pH be controlled

A

using a water bath with the temperature as close to optimum as possible
using a buffer solution as close to optimum

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20
Q

what happens during semi-conservative replication of DNA

A
  1. DNA helicase breaks the hydrogen bonds between bases to unzip DNA
  2. DNA nucleotides align with their complementary bases and DNA polymerase creates phosphodiester bonds that join nucleotides together
  3. DNA ligase joins the partly formed strands together
  4. 2 identical daughter strands are created - 1 old and 1 new
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21
Q

what did the conservative DNA replication model mean

A

1 whole completely new double helix is synthesised

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22
Q

what did the dispersive/fragmentary DNA replication model mean

A

the new DNA molecule was created as a mix of old and new parts

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23
Q

what does the induced fit hypothesis state

A

enzyme changes shape to fit substrate when substrate is near while lock and key model theorizes that the enzyme and substrate are always complementary in shape and the enzyme doesn’t change shape

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24
Q

what are enzymes

A

biological catalysts

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25
Q

how do enzymes accelerate rates of reaction

A

Lower activation energy by providing a lower energy pathway, a more favourable pH in the active site
using charge to put strain in bonds to break them
bring reactants together by using charge so that bonds form more easily

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26
Q

what types of proteins are enzymes

A

globular

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27
Q

what are intracellular enzymes

A

enzymes that work inside the cell
e.g. DNA polymerase

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28
Q

what are extracellular enzymes

A

enzymes that work outside the cell
e.g. digestive enzymes

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29
Q

Explain Lock and Key Theory

A
  1. Random movement causes enzyme and substrate to collide and the substrate enters the active site.
  2. Enzyme-substrate complex forms = shared groups attract, distort the substrate and aid in bond breaking/formation
  3. Products are released from active site, leaving it undamaged and ready to accept a new substrate
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30
Q

what does structure of a protein determine

A

its function

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30
Q

what type of protein is haemoglobin

A

globular

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30
Q

what type of protein is collagen

A

fibrous

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31
Q

describe structure of haemoglobin

A

globular with 4 polypeptide chains -2 alpha and 2 beta - each containing a haem prosthetic group

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31
Q

what 2 types of secondary structure are there

A

alpha helix or beta pleated sheet

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31
Q

describe the structure of collagen

A

fibrous with 3 polypeptides - 2 alpha and 1 beta

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32
Q

how is a tertiary structure of a protein created

A

alpha helix / beta pleated sheet fold further and create a new structure held together by disulphide bridges and ionic bonds between R groups

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32
Q

how is the quaternary structure of a protein created

A

folded polypeptides joined by hydrogen bonds - disulphide bridges and ionic binds between R groups

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32
Q

what is the general formula for an amino acid

A

a central carbon, a hydrogen, an amine group (NH2) and a carboxylic acid (COOH)

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33
Q

how are peptide bonds created

A

the OH in the carboxyl joins the H in another amino acid in a condensation reaction to remove water and form peptide bonds

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34
Q

what is the primary structure of a protein

A

sequence of amino acids

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35
Q

how does secondary structure of a protein formed

A

amino and carboxyl groups carry small amounts of charge
charge is negative on the CO and positive on the NH
result in H bonds forming between parts of the chain to stabilize the structure - alpha helix and beta pleated sheet

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36
Q

describe the role of tRNA in the production of protein part of a glycoprotein

A

each tRNA brings a specific amino acid to the ribosome
the tRNA with the complementary anticodon binds to mRNA codon
tRNA bonds to ribosome

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37
Q

compare and contrast the process of transcription with the process of DNA replication

A

Similarities:
involve formation of a polynucleotide
involve DNA helicase
Differences:
transcription uses RNA polymerase whereas replication uses DNA nucelotides
transcription uses RNA polymerase whereas replication uses DNA polymerase
transcription produces a single strand of mRNA/only copies template strand of DNA whereas replication produces double stranded DNA/ copies both strands of DNA

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38
Q

explain how change of 1 amino acid could lead to a change in the structure and properties of haemoglobin protein

A

different sequence of amino acids/primary structure
a different amino acid will have a different R group therefore secondary/tertiary/quaternary structure will change due to a change in a hydrogen bond holding the molecule in its 3D shape
haemoglobin may not bond to oxygen

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39
Q

describe the role of tRNA in the production of leptin

A

tRNA molecules transport amino acids to the ribosome
tRNA molecules has an anticodon that bonds to/recognises a codon on each mRNA
each tRNA carries a particular amino acid

40
Q

describe how the primary structure of a protein allows it to be soluble

A

primary structure/ sequence of amino acids determines the folding of polypeptides
forming globular structure
hydrophobic R groups located in the centre of the protein/ hydrophilic r groups on the outside
water forms hydrogen bonds with protein/ hydrophilic groups

41
Q

describe how a frameshift mutation could result in the production of leptin with a variety of shorter primary structures

A

adding/removing one or 2 nucleotides changes the triplet code
introducing a new stop/start codon
coding for a shorter sequence of amino acids

42
Q

describe how mRNA is synthesised at a template strand of DNA

A

RNA nucleotides align with complementary bases on DNA
RNA nucleotides joined together by RNA polymerase

43
Q

describe the differences between DNA and RNA

A

DNA:
double stranded
contains deoxyribose sugar
contains thymine as a group
RNA:
single stranded
ribose sugar
contains uracil as a group

44
Q

explain why deletion and substitution have different effects on protein structure

A

deletion could affect every codon on the mRNA/ substitution will only affect 1 codon
deletion is more likely to affect the position of a stop/start codon
deletion results in a different sequence of amino acids/ substitution may not affect sequence of amino acids
substitution may code for same amino acid
due to degenerate nature of genetic code

45
Q

explain why antibiotics that bind to ribosomes could affect the production of proteins in bacteria

A

ribosome shape is altered
mRNA is prevented from binding to the ribosome/causing change in the tRNA binding
therefore translation cannot occur
protein/polypeptide isn’t synthesised

46
Q

why might ribosome-binding antibiotics be used to treat bacteria that are resistant to other antibiotics

A

bacteria have not been exposed to new antibiotics before/ bacteria don’t have mechanisms to make them resistant to other new antibiotics
bacteria have developed resistance to other antibiotics by evolving
therefore there has been no advantage to possessing a mutation to bypass the new antibiotic

47
Q

describe the role of the CFTR protein in ensuring that the mucus produced in the lungs has the right consistency

A

Cl- ions leave the cells
Na+ ions leave the cells
increasing the solute concentration
water moves out of the cell and into mucus by osmosis

48
Q

describe the roles of transcription and translation in the synthesis of a globular protein by a muscle cell

A

the gene/ sequence of DNA for the globular proteins is transcribed
complementary base pairing between RNA nucleotides and DNA
mRNA leaves the nucleus and attaches to a ribosome
pairing between codons on mRNA and anticodons on tRNA
tRNA provides specific amino acids
the sequence of bases/codons determines the sequence of amino acid/ primary structure of the protein

49
Q

compare and contrast the structure of ATP and a DNA nucleotide

A

Both:
contain phosphate, pentose sugar and a base
Differences:
a DNA nucleotide contains deoxyribose whereas ATP contains ribose
a DNA nucleotide could contain other bases whereas ATP only contains ATP
a DNA nucleotide contains 1 phosphate whereas ATP contains 3 phosphates/ is a triphosphate

50
Q

explain the importance of primary structure functioning of ATPase

A

primary structure determines interaction between amino acids/ R groups
primary structure determines folding/ tertiary structure
therefore affecting shape of active site which would be complementary to ATP

51
Q

Factor VIII is involved in blood clotting
Explain how a change in the primary structure of VIII could cause difficulties with blood clotting

A

a different primary structure results in a different sequence of amino acids
change in R group changes folding/ bonding/ secondary structure/ tertiary structure
changing shape/charge of the active site prevents a substrate from being able to bind
stopping/reducing production of fibrin

52
Q

why are enzymes described as biological catalysts

A

they lower the activation energy and speed up the rate of biological reactions

53
Q

describe what happens to proteins following translation until release form cell

A

proteins folded in the rough endoplasmic reticulum
proteins packaged and transported in vesicles
proteins then modified in the Golgi apparatus
leave via exocytosis

54
Q

explain why enzymes that are incorrectly folded cannot carry out their function

A

the tertiary structure/ 3D shape would be different
therefore the active site of the enzyme would not fit/bind with the substrate/ would not be able to form an enzyme-substrate complex
therefore unable to catalyse reactions

55
Q

describe how an enzyme could break down the polysaccharide components

A

hydrolysis of glycosidic bonds

56
Q

compare and contrast molecular structure of globular and fibrous proteins

A

Both:
chains of amino acids
contain H bonds holding their 3D structures
Differences:
Globular have hydrophilic groups on the outside whereas Fibrous have hydrophobic groups on the outside
Globular have lots of tertiary structure and fibrous have little/no tertiary structure

57
Q

describe how the structure of phospholipase allows it to hydrolyse phospholipids

A

different sequence of amino acids
a different R group
secondary/ tertiary/ quaternary structure will change
due to a hydrogen bond changing
haemoglobin may not bind to oxygen

58
Q

give 2 differences between endocytosis and exocytosis

A

exocytosis - involves molecules/substances leaving the cells, involves vesicles fusing with cell surface membrane
endocytosis - involves molecules/substances entering the cells, involves formation of vesicles

59
Q

explain why betalain molecules cannot move through intact cell membrane

A

too large to move through the cell membrane
there are no carrier/channel proteins for betalains to move through
they’re also polar and are repelled by the hydrophobic fatty acid tails/ cannot move through fatty acid tails

60
Q

hydrolysis

A

breaking a chemical bond between 2 molecules involving a water molecule

61
Q

fibrous proteins

A

long chain proteins that are insoluble and usually have structural roles
have hydrophobic r groups on the outside have little tertiary structure

62
Q

condensation reaction

A

a type of reaction that bonds 2 molecules together with the removal of water and the formation of a chemical bond

63
Q

dipeptide

A

a molecule formed by the condensation of 2 amino acids

64
Q

primary structure

A

sequence of amino acids

65
Q

secondary structure

A

formation of alpha helixes or beta pleated sheets

66
Q

tertiary structure

A

the way a protein folds into a 3D structure

67
Q

hydrogen bond

A

a weak bond formed between a slightly positive hydrogen and a slightly negative oxygen/other atom

68
Q

what is haemoglobin

A

an example of a globular protein
used to transport oxygen
made up of 4 polypeptide chains each containing a haem group

69
Q

collagen

A

example of a fibrous protein, provides strength to many different cell types and make up connective tissues

70
Q

what is an intracellular enzyme

A

enzyme that works within the cell

71
Q

what is an extracellular enzyme

A

an enzyme that works outside of the cell

72
Q

what is ribosomal RNA

A

RNA that makes up ribosome

73
Q

what is a ribosome

A

an organelle found in the cytoplasm that carries out protein synthesis

74
Q

what is the function of an R group

A

a side chain that is attached to a molecule that determines chemical properties

75
Q

what is the importance of hydrogen bonds

A

affects how many bonds form and where, will affect secondary and tertiary structure

76
Q

what is the importance of hydrophobic and hydrophilic amino acid side group chains

A

hydrophilic = soluble in water, can affect water potential when dissolved in blood plasma
hydrophobic = insoluble in water, has no water effect

77
Q

how do ionic bonds form

A

between oppositely charged side chains on different amino acids

78
Q

what are peptide bonds

A

the bonds that are formed between amino acids

79
Q

what is the structure of a phospholipid

A

1x glycerol
2x fatty acids
1x phosphate group

80
Q

which part of a phospholipid is hydrohpilic and which is hydrophobic

A

head = hydrophilic - interacts with water
tail = hydrophobic - made up of hydrocarbons

81
Q

what happens when many phospholipids interact with water

A

create spherical clusters with tails facing inwards to shield themselves from the water with their glycerol heads
forms a bilayer/micelle

82
Q

what does the phospholipid bilayer make up

A

cell surface membrane

83
Q

what are some features of the phospholipid bilayer

A

selectively permeable - allows small, non-polar molecules to cross
has a hydrophobic barrier won’t allow large non-polar/polar to cross

84
Q

why is the fluid mosaic model named this way

A

membrane is fluid and has a mosaic like arrangement of proteins

85
Q

how much mass of a membrane is made up of proteins

A

between 25% and 75%

86
Q

what kind of proteins are in the membrane

A

integral and peripheral proteins

87
Q

what are integral proteins and what do they do

A

they span the width of the membrane and help to transport substances that cannot diffuse across the membrane but are still vital to the cells functioning
eg glucose through carrier protein through facilitated diffusion

88
Q

what a peripheral proteins and what do they do

A

confined to inner and outer surface of the membrane
may be free or bound to an integral protein
proteins on the extracellular side of membrane act as transmitters/involved in cell recognition

89
Q

what are glycoproteins

A

protein molecules with polysaccharides attached

90
Q

what factors affect membrane fluidity

A

cholesterol and temperature

91
Q

how does cholesterol affect membrane fluidity

A

vital in controlling membrane fluidity
the more cholesterol, the less fluid - more rigid and less permeable
has a hydrophobic region so its able to create a further barrier to polar substances moving through its membrane
binds to hydrophobic tail of a phospholipid, causing them to pack more closely together which restricts their movements
helps maintain shape of animal cells - RBCs

92
Q

how does temperature affect membrane fluidity

A

temp below 0 degrees - increases permeability, phospholipids are packed closely together and the membrane is rigid, channel and carrier proteins denature and ice crystals form which could pierce the membrane

temp between 0-45 degrees - phospholipids can move and aren’t as tightly packed, membrane is partially permeable, as temp increases phospholipids can move more because they have more energy

temps above 45 - phospholipid bilayer starts to melt, water inside cells expands which putting more pressure on membrane, the channel and carrier proteins denature

93
Q

define facilitated diffusion

A

the overall net movement of molecules and ions from a region of high concentration to a region of low concentration down a concentration gradient

94
Q

what is the type of some proteins that are involved in facilitated diffusion

A

carrier proteins

95
Q

what happens when an ion/molecule binds to a carrier protein

A

it changes shape and therefore the molecule is able to cross the molecule

96
Q

what is another name for diffusion

A

passive transport as it uses no energy

97
Q

define active transport

A

movement of molecules/ions from an area of low concentration to an area of high concentration against a concentration gradient, using energy from ATP

98
Q

where is the energy for active transport sourced from

A

adenosine triphosphate

99
Q

how is ATP formed and how is it used

A
  1. it is formed during respiration, the breakdown of energy store molecules
  2. the substances to be transported across the membrane binds to the carrier protein
  3. one phosphate group is removed from ATP by hydrolysis and ADP forms
  4. a small amount of energy is required to break the bond holding the end phosphate in ATP
  5. once removed, phosphate group becomes hydrated
    lots of energy is released as bonds form between water and phosphate
100
Q

how is a phosphate group removed from ATP

A

hydrolysis

101
Q

what is ADP

A

adenosine diphosphate

102
Q

how is active transport sometimes referred to as

A

pumping
the pumping of substances across membranes that occurs in every cell

103
Q

what is a glycolipid

A

a lipid with polysaccharides attached via glycosidic bonds

104
Q

what processes are used when large molecules/quantities of molecules need to be transported across a membrane

A

endocytosis
exocytosis

105
Q

what is a vesicle

A

small membrane bound sacs containing substance

106
Q

what is the process of exocytosis

A

vesicles fuse with the cell membrane and the contents are released

107
Q

what is an example of exocytosis

A

insulin is released to the blood via exocytosis

108
Q

what is the process of endocytosis

A
  1. substances are taken into the cell by the creation of a vesicle from the cell surface membrane
  2. part of the membrane engulfs the solid/liquid material to be transported
  3. in some cases, the substances which is to be absorbed, attaches itself to a receptor in the membrane and is then absorbed by endocytosis
109
Q

what is an example of endocytosis

A

cholesterol being taken in by cells
white blood cells ingesting bacteria

SNAB Biology Edexcel (5 decks)

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