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Biology Year 1 > Topic 2 > Flashcards

Topic 2 Flashcards

1
Q

what is cystic fibrosis?

A

a genetic disorder in which abnormally thick and sticky mucus is produced in the lungs and other parts of the body.

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2
Q

what is the cause of cystic fibrosis?

A

a faulty recessive allele of the gene that codes for the transporter protein CFTR.

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3
Q

how is cystic fibrosis diagnosed?

A
  • a sweat test (to measure the amount of salt in sweat which would be abnormally high in patients with CF).
  • a genetic test (a sample of blood or saliva is tested for the faulty allele).
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4
Q

what are the properties of gas exchange surfaces in living organisms?

A
  • LARGE SURFACE AREA TO VOLUME RATIO (large objects have a smaller surface area to volume ratio than small objects. the smaller the surface area to volume ratio the slower the rate of exchange).
  • THICKNESS OF SURFACE (the rate of diffusion is inversely proportional to the thickness of the gas exchange surface. a thin surface provides a short diffusion pathway).
  • DIFFERENCE IN CONCENTRATION (a steep gradient in oxygen and carbon dioxide concentration allows a faster rate of diffusion).
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5
Q

how can the rate of diffusion be calculated using Fick’s Law?

A

rate of diffusion is proportional to
surface area x difference in concentration / thickness of gas exchange surface.
- rate of diffusion is directly proportional to surface area.
- rate of diffusion is directly proportional to the difference in concentration across the gas exchange surface.
- rate of diffusion is inversely proportional to the thickness of the gas exchange surface.

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6
Q

how is the structure of the mammalian lung adapted for rapid gaseous exchange?

A
  • THIN BARRIER TO REDUCE DIFFUSION DISTANCE: the alveolus epithelium is one cell thick, the capillary endothelium is one cell thick, the capillaries are in close contact with the alveolus walls.
  • LARGE SURFACE AREA provided by lots of alveoli.
  • A STEEP CONCENTRATION GRADIENT maintained by ventilation and blood flow.
  • extensive capillary network around each alveoli provides large surface area for gas exchange.
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7
Q

what is the structure and properties of a cell surface membrane?
(phospholipid bilayer)

A

consists of a PHOSPHOLIPID BILAYER.
HYDROPHOBIC TAILS orientates itself away from water towards the centre of the membrane.
HYDROPHILIC HEADS orientates itself towards water.
lipid-soluble material moves through the membrane via the phospholipid portion.
water soluble substances are prevented from entering and leaving the cell.
the phospholipid bilayer makes the membrane FLEXIBLE and SELF SEALING.

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8
Q

what is the structure and properties of a cell surface membrane?
(proteins)

A

EXTRINSIC PROTIENS: located on the surface of the bilayer. act as mechanical support or in conjunction with glycolipids as cell receptors.
INTRINSIC PROTEINS: span the phospholipid bilayer. protein channels allow water soluble ions to diffuse across the membrane. carrier proteins bind to ions or molecules then change shape in order to move the molecule across the membrane.

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9
Q

what is the structure and properties of the cell surface membrane?
(cholesterol)

A

these molecules are hydrophobic.
prevent lateral movement.
make the membrane less fluid at higher temperatures.
prevent leakage of water and dissolved ions from the cell.

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10
Q

what is the structure and properties of the cell surface membrane?
(carbohydrate chains)

A

GLYCOLIPIDS: made up of carbohydrate chains covalently bonded with a lipid. act as recognition sites. maintain the stability of the membrane. help cells to attach to one another to form tissues.
GLYCOPROTEINS: carbohydrate chains attached to extrinsic proteins. act as recognition sites (hormones). help cells to attach to one another to form tissues. allows cells to recognise from one another e.g. lymphocytes.

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11
Q

describe the fluid mosaic model as an explanation of the structure and properties of the cell surface membrane.

A

FLUID: the individual phospholipid molecules can move relative to one another. this gives the membrane a flexible structure that is constantly changing shape.
MOSAIC: the proteins are embedded in the phospholipid bilayer and vary in shape, size and pattern.

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12
Q

what is osmosis?

A

the diffusion of free water molecules across a partially permeable membrane from an area of higher concentration of water molecules to an area of lower concentration of water molecules.

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13
Q

what is meant by passive transport?

A

no metabolic energy is required for it to happen.
the process is driven by the concentration gradient itself.
(diffusion and facilitated diffusion)

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14
Q

what is diffusion?

A

the net movement of particles from an area of higher concentration to an area of lower concentration.
particles diffuse down a concentration gradient.

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15
Q

what is facilitated diffusion?

A

diffusion through carrier proteins or channel proteins.

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16
Q

how are carrier proteins involved in membrane transport?

A

move large hydrophilic molecules into or out of a cell down a concentration gradient.
the ion or molecule binds onto a specific site on the protein.
the protein changes shape and as a result the ion or molecule crosses the membrane.

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17
Q

how are channel proteins involved in membrane transport?

A

polar molecules or ions diffuse through water filled pores within the channel protein.
each type of channel protein has a specific shape that permits the passage of only one type of ion or molecule.
some channel proteins can be opened or closed depending on the presence or absence of a signal e.g. a hormone (these channels are called gated channels).

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18
Q

describe active transport.

A

uses energy in the form of ATP to move molecules and ions across plasma membranes against a concentration gradient. this process involves carrier proteins.
ATP is produced by respiration and acts as an immediate source of energy in a cell.
when ATP is hydrolysed in the cell, energy is released.

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19
Q

describe endocyctosis.

A

some molecules are too large to be taken into a cell by carrier proteins.
a cell instead can surround a substance with a section of its cell membrane.
the membrane then pinches off to form a vesicle inside the cell containing the ingested substance.
this process also uses ATP for energy.

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20
Q

describe exocytosis.

A

some substances produced by the cell need to be released.
vesicles containing these substances pinch off sacs of the Golgi apparatus and move towards the cell membrane.
the vesicles fuse with the cell membrane and release their contents outside the cell.
this process uses ATP as an energy source.

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21
Q 
describe:
monomer
dipeptide
polypeptide 
protein
A

the monomer of proteins are AMINO ACIDS.
a dipeptide is formed when two amino acids join together.
a polypeptide is formed when more than two amino acids join together.
proteins are formed when one or more polypeptide chains fold into a specific shape that allows it to perform a specific function.

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22
Q

what is the general structure of an amino acid?

A

a central carbon (C) atom bonded to a carboxyl group (-COOH), an amine group (-NH2), a hydrogen atom (-H) and an R group (-R).

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23
Q

what varies between each amino acid?

A 
the R group is different in each amino acid.
it can vary by:
size
polarity 
charge
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24
Q

how is a dipeptide formed?

A

two amino acids are joined together by a CONDENSATION REACTION to form a dipeptide.
the condensation reaction occurs between the CARBOXYL GROUP (-COOH) and the AMINE GROUP (-NH2) on adjacent amino acids.
a molecule of water is released as one oxygen and two hydrogen atoms are removed from the amino acids.
this creates a PEPTIDE BOND.

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25
Q

what type of bond is a peptide bond?

A

a covalent bond formed when two amino acids are joined together in a condensation reaction.

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26
Q

how is a polypeptide formed?

A

many amino acids can be joined together in a series of CONDENSATION REACTIONS to form a polypeptide.

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27
Q

what is a polypeptide?

A

a POLYMER made of many amino acids joined together by PEPTIDE BONDS through a series of CONDENSATION REACTIONS.

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28
Q

what is meant by a buffer?

A

amino acids acts as a buffer ( a solution that resists pH change).
too acidic = to many H+ ions.
too alkali = not enough H+ or too many OH- ions.

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29
Q

what is meant by a hydrolysis reaction?

A

a dipeptide can be broken down into two amino acids through a hydrolysis reaction.
a hydrolysis reaction requires water as one oxygen and two hydrogen atoms are added to the dipeptide.
this breaks the peptide bond forming two amino acids.
polypeptides can be broken down into amino acids by a series of hydrolysis reactions.

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30
Q

what is meant by the primary structure of a protein?

A

the specific sequence of amino acids in the polypeptide.

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31
Q

describe the primary structure of protein.

A

when a polypeptide is formed, the order of amino acids determines the primary structure of a protein .
there are 20 different naturally occurring amino acids.
every protein has a unique primary structure therefore function.

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32
Q

what is meant by the term secondary structure of a protein?

A

the polypeptide chain folding into either an alpha helix or beta pleated sheet, held together by hydrogen bonds.

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33
Q

describe the secondary structure of a protein?

A

polypeptides can fold in two main ways:
alpha helix ( a coil)
beta pleated sheets (a zig-zag folded over itself)
all amino acids in the polypeptide chain contain a -C=O group and a -NH group when bonded.
the hydrogen in the -NH is slightly positive and the oxygen in the -C=O is slightly negative resulting in hydrogen bonds between the amino acids in the polypeptide chain.

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34
Q

are hydrogen bonds strong or weak?

A

hydrogen bonds are weak but the many hundreds of them keep the secondary structure stable.

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35
Q

what is meant by the term tertiary structure of a protein?

A

the specific interaction of folding into the specific 3D shape driven by the bonds formed between the R groups of the amino acids.

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36
Q

describe the different bonds formed between R groups in the tertiary structure.

A

HYDROGEN BONDS form between POLAR (delta positive and delta negative) R groups.
IONIC BONDS form between POSTIVE and NEGATIVELY charged R groups.
DISULPHATE BRIDGES form between SULPHUR atoms in R groups.

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37
Q

what else determines the 3D structure of the protein?

A

Amino acids with HYDROPHOBIC R groups tend to be found in the centre of the protein.
Amino acids with HYDROPHILIC R groups tend to be found on the outside of the protein.
all determine the specific 3D structure of a protein.

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38
Q

why are the properties of amino acid R groups so important?

A

the overall 3D structure of a protein is a result of properties and therefore interactions.
the primary structure determines the tertiary structure.

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39
Q

what is meant by the term the quaternary structure of a protein?

A

the specific 3D shape that is determined by the multiple polypeptide chains and/or prosthetic groups bonded together.

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40
Q

describe the quaternary structure of a protein?

A

the polypeptide chains are held together in by hydrogen bonds, ionic bonds and disulphide links.
non-protein groups (prosthetic groups) may also be associated with the polypeptide chains forming conjugated proteins.
a conjugated protein have another chemical group associated with their polypeptide chain(s).

41
Q

what is the significance of the primary structure of a protein?

A

the amino acid sequence of a protein determines what bonds will form and how the protein will fold up into its 3D structure.
the 3D structure of a protein determines its properties.
its properties relate to its function in the body.

42
Q

describe globular proteins.

A

round and compact made up of multiple polypeptide chains.
soluble due to hydrophilic side chains that project from the outside of the molecule and are important in metabolic reactions.
e.g. enzymes
roles in binding to other substances (transport proteins within membranes, haemoglobin in red blood cells).

43
Q

describe fibrous proteins.

A

remain as long chains.
several polypeptide chains can be cross-linked for additional strength.
insoluble.
important structural molecules (e.g. collagen)
cross-linked strands are staggered avoiding the creation of any weak points along the length of the molecule.

44
Q

what is a gene?

A

a sequence of bases on a DNA molecule that codes for the sequence of amino acids in a polypeptide chain.

45
Q

what is DNA?

A

a nucleic acid storing genetic information.

deoxyribonucleic acid

46
Q

what is a chromosome?

A

DNA wound around histone proteins for storage.

47
Q

what is RNA?

A

a nucleic acid that transfers genetic information from the DNA to the ribosomes.
ribosomes are made of RNA and proteins.
(ribonucleic acid)
RNA only has one strand.

48
Q

what is a mononucleotide?

A

a molecule made from:
a pentose sugar (has 5 carbon atoms and is either ribose of deoxyribose)
a nitrogenous base
a phosphate group
mononucleotides are linked through condensation reactions.

49
Q

what are the nitrogenous bases?

A 
adenine (DNA and RNA)
guanine (DNA and RNA)
cytosine (DNA and RNA)
thymine (DNA only)
uracil (RNA only)
50
Q

how is a polynucleotide formed?

A

mononucleotides join together by CONDENSATION REACTIONS between the sugar of one nucleotide and the phosphate of the next one producing a polynucleotide held together by PHOSPHODIESTER BONDS.

51
Q

describe the structure of DNA.

A

two polynucleotide strands twist around each other to form a DOUBLE HELIX.
the sugars and phosphates form the two SUGAR PHOSPHATE BACKBONES.
the bases point inwards horizontally and are held together in complementary base pairs by HYDROGEN BONDS, keeping the two strands coiled together.
the two polynucleotide strands are describe as being ANTIPARALLEL as they run in opposite directions (5’, 3’ and 3’, 5’).

52
Q

why does the base A only pair with T and C only pair with G in DNA?

A

Purines (G and A) are double ringed structures.
Pyrimidines (C and T) are single ringed structures,
Purines always pair up with pyrimidines.
The bases pair so that there are three rings forming each rung of the DNA molecule, making it uniform along its whole length.
Two hydrogen bonds form between A and T and three hydrogen bonds form between C and G in complementary base pairings.
This is due to there being a definite width between the sugar phosphate backbones otherwise the two strands cannot twist into a double helix.

53
Q

describe stage 1 of polypeptide synthesis

transcription

A

1) RNA polymerase attaches to the DNA double helix.
2) the hydrogen bonds between the two DNA strands break and the DNA molecule unwinds.
3) the RNA polymerase lines up free RNA nucleotides alongside the template (antisense) strand.
4) once the RNA mononucleotides have been paired up with their complementary base, phosphodiester bonds form to produce a mRNA molecule with the same base sequence as the DNA coding (sense) strand.
5) the mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm.

54
Q

describe stage 2 of polypeptide synthesis

translation

A

1) the mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome.
2) a tRNA molecule, with an anticodon that is complementary to the start codon on the mRNA, attaches itself to the mRNA by complementary base pairing.
3) a second tRNA molecule attaches itself to the next codon on the mRNA in the same way.
4) the two amino acids attached to the tRNA molecule are then joined together by a peptide bond. the first tRNA molecules moves away leaving its amino acid behind.
5) the ribosome moves along to the next codon.
6) the process continues producing a polypeptide chain until it reaches the stop codon on the mRNA molecule.

55
Q

describe the nature of the genetic code.

A

degenerate
non-overlapping
triplet code

56
Q

what does a degenerate genetic code mean?

A

there are 20 amino acids to be coded for and 64 base triplets to use to code them.
each amino acid has more than one codon therefore the genetic code is degenerate.

57
Q

why is the genetic code a triplet code?

A

three bases code for one amino acid, 64 amino acids could be coded for which is more than enough. the genetic code is a triplet code.

58
Q

how is the genetic code non overlapping?

A

each base is only read once and each base is only part of one triplet.

59
Q

what is the start codon and what amino acid does it code for?

A

AUG

codes for the amino acid methionine.

60
Q

what are the stop codons?

A

UAA, UAG, UGA
no complementary anticodon on tRNA molecules.
there is no AUU, AUC and ACU anticodons.

61
Q

what are enzymes?

A

biological catalysts that reduce activation energy.

62
Q

what are two ways an enzyme can reduce the activation energy of a biological reaction by forming an enzyme-substrate complex?

A

1) if the two substrate molecules need to be joined, being attached to the enzyme holds them closer together, reducing any repulsion between the molecules so they can bond more easily.
2) if the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate, so the substrate molecule breaks up more easily.

63
Q

how does the 3D structure of an enzyme relate to it’s mechanisms of action and specificity?

A
  • properties relate to their TERTIARY STRUCTURE.
  • only one complementary substrate will fit into the active site.
  • the active sites shape is determined by the tertiary structure which is determined by the primary structure.
  • the tertiary structure of an enzyme may be altered by changes in pH or temperature.
  • the primary structure of a protein is determined by a gene therefore if a mutation occurs in that gene it could change the tertiary structure of the enzyme produced.
64
Q

how does enzyme concentration and substrate concentration affect enzyme activity?

A

increasing enzyme concentration will speed up the rate of reaction, as long as there is substrate available to bind to.
increasing substrate concentration will speed up the rate of reaction up to a certain point (once all the enzymes have bound).

65
Q

what are intercellular enzymes?

A

enzymes which catalyse reactions inside cells for example DNA polymerase, RNA polymerase.

66
Q

what are extracellular enzymes?

A

enzymes which catalyse reactions outside of cells for example digestive enzymes, salivary amylase.

67
Q

describe the process of semi-conservative DNA replication.

A

1) helicase breaks the hydrogen bonds between complementary bases on two polynucleotide DNA strands. the double helix unwinds.
2) each original single strand acts as a template for a new strand. free floating nucleotides are activated and are attracted to their exposed complementary bases on each original template strand.
3) hydrogen bonds form between the two complementary bases.
4) phosphodiester bonds form between the phosphate and deoxyribose sugar in a condensation reaction catalysed by DNA polymerase.
5) nucleotides can only be added in the 5’ to 3’ direction meaning that the leading strand’s nucleotides are assembled continuously whereas on the lagging strand, Okazaki fragments are created. these fragments are later joined to form one continuous length.
6) two daughter strands are now produced. each cell will contain one original and one daughter strand.

68
Q

how has Meselson and Stahl’s classic experiment provided new data that supported the accepted theory of DNA replication?

A

before Meselson and Stahl’s experiment scientists were unsure whether DNA replication was semi-conservative or conservative.
if the method was conservative, original DNA strands would stay together and the new DNA molecules would contain two new strands.
Meselson and Stahl showed that DNA replication was semi-conservative by using two isotopes of nitrogen (DNA contains nitrogen):
- heavy nitrogen (15N)
- light nitrogen (14N)

69
Q

what were the results of Meselson and Stahl’s experiment?

A

DNA settled out in the middle of the centrifuge tube showing that the DNA molecules contained a mixture of heavy and light nitrogen. the bacterial DNA had replicated semi-conservatively in the light nitrogen.

70
Q

what are silent mutations?

A

when substitution of a base still codes for the same amino acid as the original base due to the degenerate nature of the genetic code.
this mutation would have no effect.

71
Q

what are nonsense mutations?

A

when a substitution of a base occurs leading to a PREMATURE STOP CODON being coded for.
this would lead to the premature end to the synthesis of a polypeptide.
successful synthesis of the final protein would be very unlikely.

72
Q

what are mis-sense mutations?

A

when a change in base leads to a different amino acid being coded for.

73
Q

what is a deletion of bases mutation?

A

when a nucleotide is lost from the DNA sequence.
deleting a base can lead to the codons not being read properly.
this is due to the triplet code.
usually the amino acid sequence of the new code will be entirely different.

74
Q

describe the mutation which lead to cystic fibrosis?

A

CF is caused by a mutant recessive allele caused by a DELETION MUTATION of three bases (AAA) in the CFTR gene which codes for the CFTR protein.

75
Q

what is the role of the CFTR protein and what happens for CF sufferers?

A

to transport Cl- ions across epithelial cell membranes.
water then follows by osmosis so membranes are kept moist and the mucus runny.
in sufferers of CF, CFTR is non-functional so water is retained in the cell by the high concentration of chloride ions as they are unable to leave the cell therefore the membrane is dry and the mucus very sticky.

76
Q

what is the meaning of gene?

A

a section of DNA which codes for a polypeptide, found at a particular locus.

77
Q

what is the meaning of allele?

A

a different form of a gene that codes for a different version of a characteristic.

78
Q

what is the meaning of genotype?

A

a description of the pair of alleles present for a characteristic.

79
Q

what is the meaning of phenotype?

A

the physical expression of the alleles.

80
Q

what is the meaning of recessive?

A

an allele that will only be expressed when both alleles are of this type.

81
Q

what is the meaning of dominant?

A

an allele that will always be expressed even when there is only one of these alleles present.

82
Q

what is the meaning of incomplete dominance?

A

a cross between organisms with two different phenotypes which produce offspring with a third phenotype that is a blending of the parental traits.

83
Q

what is the meaning of homozygous?

A

pair of alleles that produce a characteristic that are the same e.g. HH, hh

84
Q

what is the meaning of heterozygous?

A

pair of alleles that produce a characteristic that are different e.g. Hh

85
Q

how does the genetic mutation in people with CF impair the functioning of the gaseous exchange system?

A

the cilia are unable to move the mucus towards the throat because it is so thick and sticky.
this means the mucus builds up in the airways.
gas exchange cannot take place in the area below if the airways become blocked.
the surface area available for gas exchange is reduced, causing breathing difficulties.
also prone to lung infections as mucus containing microorganisms cannot be removed.

86
Q

how does the genetic mutation in people with CF impair the functioning of the digestive system?

A

the pancreatic duct becomes blocked with mucus preventing digestive enzymes reaching the small intestine.
this reduces the ability to digest food and fewer nutrients can be absorbed.
the mucus can cause cysts in the pancreas inhibiting the production of digestive enzymes.
the mucus lining the small intestine is abnormally thick inhibiting the absorption of nutrients.

87
Q

how does the genetic mutation in people with CF impair the functioning of the reproductive system?

A

in men, the tubes connecting the testicles to the penis absent or can become blocked so sperm produced can’t reach the penis.
in women, thickened cervical mucus can prevent the sperm from reaching the egg.
thick mucus reduces the motility f the sperm, reducing its chances of making it to the egg.

88
Q

what are the three main uses of genetic screening?

A

identification of carriers
preimplantation genetic diagnosis (PGD)
prenatal testing

89
Q

what are the ethical concerns of the identification of carriers?

A

may cause emotional stress or affect your ability to find a partner.
the tests are not always 100% accurate and could give false results.
other genetic abnormalities could be found which could cause further stress.
could result in genetic discrimination.

90
Q

how is preimplantation genetic diagnosis carried out?

A

PGD is carried out on embryos produced by IVF.

it involves the screening embryos for genetic disorders before they’re implanted into the women.

91
Q

what are the advantages of PGD?

A

reduces the chance of having a baby with a genetic disorder- only embryos without the genetic disorder will be implanted.
since it is performed before implantation it avoids the issue of abortion that could be raised by prenatal testing.

92
Q

what are the ethical issues of PGD?

A

it can be used to find out other characteristics e.g. gender and eye colour leading to concerns that in the future embryos may be selected for desired characteristics (designer babies).
false results could provide incorrect information.

93
Q

what are the two types of prenatal testing?

A

amniocentesis

chorionic villus sampling

94
Q

describe amniocentesis.

A

carried out at 15-20 weeks of pregnancy.
a sample of amniotic fluid is obtained via the abdomen using a very fine needle.
this fluid contains fetal cells containing DNA which can be analysed.
has a 1% risk of miscarriage.
results available after 2-3 weeks.

95
Q

describe chorionic villus sampling (CVS).

A

performed at 11-14 weeks of pregnancy.
allows the earlier decision of abortion making it potentially less traumatic than amniocentesis.
a sample of cells is taken from the chronic villi containing fetal cells which are analysed.
the procedure is done via the abdomen using a fine needle or the vagina using a catheter.
1-2% risk of miscarriage.
detailed test results can more than two weeks.

96
Q

what are the advantages of prenatal genetic screening?

A

allows parents to make informed decisions.
the parents may decide to have the child or have an abortion if the tests are positive.
the results can help parents to prepare for the future care of the child and any medical treatment available can be started at birth.

97
Q

what are the ethical issues of prenatal screening?

A

slightly increase the risk of miscarriage.
false results could provide incorrect information.
some people consider it unethical to abort a fetus because it has a genetic disorder.

98
Q

what is the effect of different ratios of phospholipids that contain saturated or unsaturated fatty acids?

A

the greater the ratio of phospholipids that contain unsaturated fatty acids to those containing saturated fatty acids, the more fluod the membrane will be. the ‘kinks’ in the hydrocarbon tails of the unsaturated phospholipids prevent them from packing closely together so more movement is possible.

Biology Year 1 (4 decks)

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