topic 2 - genes and health Flashcards
(104 cards)
1
Q
3 factors that increase rate of diffusion
A
- large surface area to volume ratio
- thin surfaces
- steep concentration gradient: greater difference in number of molecules passing in the two directions means a faster rate of diffusion
- temperature: more kinetic energy, thus molecules move faster
2
Q
how are lungs adapted for gas exchange?
A
- lots of alveoli increases surface area
- alveoli one cell thick - reduces diffusion distance
- rich blood supply to maintain conc gradient
3
Q
describe cell membrane structure
A
“fluid mosaic” structure
- phospholipid molecules form a bilayer
- phospholipid molecule contains a head containing the phosphate group (hydrophilic) and a tail made of two fatty acids (hydrophobic).
- hydrophobic heads face in meaning the membrane does not allow water soluble substances to pass
- protein molecules scattered through
- some proteins have a polysaccharide - glycoproteins
- some lipids have the same -glycolipids
- cholesterol makes membrane more rigid
4
Q
diffusion definition
A
the net movement of molecules from a region of high conc to a region of low conc down a conc gradient
- passive
5
Q
facilitated diffusion
- explain carrier and channel proteins
A
carrier proteins: move large molecules into and out of cell.
1. a large molecule attaches to carrier in membrane. 2. protein changes shape. 3. molecule released on opposite side
channel: form pores in the membrane so ions can diffuse through. each type of channel protein has a specific shape
6
Q
osmosis defintion
A
the net movement of water molecules from a solution with high water potential to low
- continues until isotonic
7
Q
active transport explain
A
- substances are moved against a conc gradient
- energy in form of ATP required
8
Q
explain endocytosis
A
- some molecules are too large to be taken in by carrier proteins. instead a cell can surround substance with a section of its membrane and form a vesicle inside the cell. requires ATP
9
Q
explain exocytosis
A
substances need to be released.
vesicles containing these substances pinch off from sacs of golgi apparatus and move towards membrane.
- vesicles fuse with membrane and release contents
- uses ATP
10
Q
proteins monomer
A
amino acids
11
Q
bond that joins amino acids
A
peptide bond
(this is covalent)
12
Q
explain primary structure
- define
- explain how this occurs
A
- the sequence of amino acids in a polypeptide chain
- two amino acids join in a condensation reaction to form a dipeptide
13
Q
explain secondary structure
A
- 2D arrangement of the chain of amino acids
- chain may twist to form an alpha helix. hydrogen bonds form between slightly neg carboxylic acid and slightly pos amine group
- chain may fold back on itself and link together with hydrogen bonds to form a beta pleated sheet. each bond is weak but there are many so structure is stable
14
Q
explain tertiary structure
A
- 3D folding of the secondary structure
- shape is determined by type of bonding present: hydrogen bonding, ionic and disulphide bridges
- chemical bonds maintain structure
-disulphide bonds are strong but sensitive to changes in pH
15
Q
explain quaternary structure
A
- 3D arrangement of more than one polypeptide
16
Q
globular proteins
- properties and structure
- example
A
- polypeptide chain folded into compact, spherical shape
- soluble due to hydrophilic side chains so easily transported
- egs include enzymes and antibodies
- HAEMOGLOBIN:
- consists of 4 beta polypeptide chains and a haem group.
- 4 polypeptide chains are held together with disulphide bonds
- water soluble
- conjugated protein as associated with another chemical group
17
Q
fibrous proteins
- structure and properties
- example
A
- long parallel polypeptides
- can be cross linked for additional strength
- insoluble due to hydrophobic R groups
- used for structure
- strong
- COLLAGEN:
- three polypeptide chains wound together and held by H bonds
- each strand cross links for strength
- strands are staggered to avoid weak points
- stable protein due to high proportion of proline and hydroxyproline amino acids present.
- strong due to hydrogen and covalent bonds
18
Q
enzymes definition
A
-globular proteins that speed up chemical reactions by acting as a biological catalyst
19
Q
lock and key theory
A
- specific substrate molecule fits into active site of enzyme
- substrate forms temporary bonds with active site to form enzyme substrate complex
- products are released
20
Q
induced fit theory
A
- when substrate enters active site, enzyme changes shape slightly
- products formed and released
21
Q
how do enzyme properties relate to tertiary structure
A
- enzymes are very specific, they only catalyse one reaction as only one complementary substrate fits active site
- active site is determined by primary structure
- each enzyme has different tertiary structure and thus a different active site
- if tertiary structure changes, active site changes and substrate wont fit
22
Q
what is tertiary structure altered by
A
- pH and temperature
23
Q
how does temp affect enzyme action
A
- increase in kinetic energy means molecules move faster, more successful collisions
- after optimum temp (40 degrees) H bonds break, and active site changes shape
- substrate no longer fits
- tertiary structure is disrupted: enzyme and active site denatures
24
Q
how does pH affect enzyme action
A
- change in pH changes H and ionic bonds on amino acids
- active site alters and substrate does not fit
- bonds holding tertiary structure break and enzyme changes shape and denatures
25
how does enzyme conc affect enzyme action
how does substrate conc affect enzyme action
- more enzyme molecules = more active sites and more successful collisions. this increases rate of reaction
- if substrate is limited adding more enzymes does nothing
- the higher the conc, the faster the reaction due to collisions. at "saturation point" all active sites are full so it no longer has an effect
26
competitive inhibitors
- binds to enzyme in active site as shape is similar to substrate
- occupies active site
27
non- competitive inhibitors
- binds to enzyme in allosteric site which changes shape of enzyme so substrate cannot fit
28
two stages of protein synthesis
transcription and translation
29
describe transcription
A MOLECULE OF mRNA IS MADE IN NUCLEUS
1. hydrogen bonds break between complementary bases and DNA uncoils into two strands
2. one DNA strand is used as a template to make mRNA. this is the antisense strand
3. free nucleotides line up by complementary base pairing and adjacent nucleotides are joined with phosphodiester bonds. forming mRNA
4. mRNA moves out nucleus through pore and attaches to a ribosome
30
name the three components of nucleotides
- pentose sugar
- phosphate group
- organic base
31
describe DNA structure
- double stranded
- made up of deoxyribose mononucleotides linked through condensation reactions
- possible bases are adenine, cystine, guanine and thymine
- c pairs with g
- a pairs with t
32
how does DNA form a double stranded helix
- bases form hydrogen bonds with each other holding two strands together
- stacking of many mononucleotides results in helix shape
33
describe RNA structure
- single stranded
- made up of many mononucleotides linked via condensation reactions
- possible bases are adenine, cystine, guanine and uracil
- c pairs with g
- a pairs with u
34
identify four features of the genetic code
- triplet of bases codes for a particular amino acid
- non overlapping : each base is only read once so the adjacent codons do not overlap
- degenerate = more than one triplet codes for the same amino acid
- universal: almost every organism uses the same code, the same triplet codes code for the same amino acids in all living things
35
gene definition
a sequence of bases on a DNA molecule that codes for a specific sequence of amino acids in a polypeptide chain
36
describe translation
1. mRNA goes to ribosome which reads sequence in codons recognised by anti codons found on tRNA which carries amino acids which join via peptide bonds to form polypeptides until a stop codon is reached
MRCATAPP
37
Explain how a change of one amino acid could lead to a change in the
structure and properties of the haemoglobin protein.
different {sequence of amino acids / primary structure} (1)
• (a different amino acid will have a) different R group (1)
• (therefore) {secondary / tertiary / quaternary} structure
will change (1)
• (due to a) change in a named bond (holding molecule in its
three-dimensional shape) (1)
• (haemoglobin) may not bond to oxygen (1)
38
Explain how the structure of a phospholipid molecule contributes to the
partial permeability of a cell surface membrane.
(phospholipid molecule) contains a {polar / hydrophilic}
(phosphate) head and {non-polar / hydrophobic} fatty acid
chains (1)
• allows {fat-soluble/non-polar} molecules to pass through (the
membrane) (1)
• {polar / ionic} molecules cannot pass through (phospholipid
bilayer) (1)
39
compare and contrast endo and exocytosis
- both involve ATP
- both involve vesicles
- one leaves one enters
40
Describe how mRNA is synthesised at a template strand of DNA.
(RNA) nucleotides align with complementary bases (on DNA) (1)
• RNA nucleotides joined together by {RNA polymerase /
phosphodiester bonds} (1)
41
explain the steps of semi conservative DNA replication
1. double helix unwinds and hydrogen bonds break between complementary bases, catalysed by DNA helicase, separating the two strands
2. one of the strands is used as a template and complementary base pairing occurs
3. adjacent nucleotides are joined by phosphodiester bonds formed in condensation reactions
42
what does semi-conservative replication of DNA do
ensures genetic continuity between generations of cells, meaning genetic information is passed on through generations
43
what is conservative replication
conserves both strands of parent DNA
44
what is dispersive replication
individual DNA strands are a mixture of old and new DNA
45
explain the meselson and stahl experiment
(proves semi-conservative replication)
- originally grew DNA in a culture containing N15 for several generations, so all the bases contained this isotope
- they then grew the DNA in a culture of N14 for one generation
- after this generation, the DNA contained one strand containing 15-N and one 14-N
- after another generation, half of the DNA molecules were the same as generation one, and the other half contained only 14-N
46
what is a mutation
permanent changes in the DNA of an organism
47
explain cystic fibrosis
- caused by mutation of a single change which codes for the CTFR protein
- CTFR= channel protein which transports chloride ions out of respiratory tract and into mucus. sodium ions then leave the cell following the chloride ions which increases the solute concentration in the mucus . water then moves out of the cells by osmosis
- mutation makes mucus very thick, causing problems in gas exchange, reproduction and digestion
48
what are the problems in the respiratory system with those who have CF
- build up of mucus in the lungs traps bacteria, increasing risk of infection
- build up of mucus in airways decreases alveoli surface area, thus reducing SA for gas exchange
49
how does CF affect the reproductive system
- cervical mucus prevents sperm from reaching egg
- in men, sperm duct is blocked with mucus, meaning sperm produced cannot leave the testes
50
how does CF affect the digestive system
- pancreatic duct becomes blocked with mucus, so digestive enzymes don't reach small intestine. fewer nutrients are absorbed
- mucus lining in duodenum is thick, reducing absorption of nutrients
- mucus can cause cysts to form in the pancreas, damaging insulin producing cells leading to diabetes
51
allele definition
one of the different forms of a particular gene found at the same locus on a chromosome
52
recessive definition
allele that only produces a feature if two copies are present
53
dominant defintion
produces a feature even if only one copy of the allele is present
54
homozygote
two identical alleles of a particular gene
55
heterozygote
two different alleles of a particular gene
56
what is a mutation
permanent changes in the DNA of an organism. mutations are changes in the arrangement of bases
57
explain the five types of mutation
substitution- change in one base
insertion - adding another base in
deletion- taking a base out
duplication- adding the same base more than once
inversion- swapping the order of bases around
58
what does a change in the base sequence result in?
results in a change to the mRNA, tRNA and therefore the primary structure of a protein
59
what are the three main uses of genetic screening ?
1. identification of carriers: offered to individuals with a family history of genetic disorders. it shows whether people carry the allele for a specific disorder.
2. preimplantation genetic diagnosis: carried out on embryos produced by IVF. involves screening embryos before they are implanted.
3. prenatal testing: involves screening unborn babies
60
what does an insertion mutation do
- a mutation occurs when a nucleotide is randomly inserted into the DNA sequence
- an insertion mutation changes the amino acid that would have been coded for as it creates a different triplet of bases
- a insertion mutation also has a knock on effect on other base triplets by changing the triplets further on in the DNA sequence
- this then changes the amino acid sequence produced and thus the ability of the polypeptide to function
61
what does a deletion mutation do
- changed the triplet in which the deletion has occurred, and changes every group of three bases further on in the DNA sequence
- this then changes the amino acid sequence produced and thus the ability of the polypeptide to function
62
what does a substitution mutation do
- changes the triplet in which the mutation occurs - DOES NOT change any other section of the DNA sequence
63
three types of substitution mutations
1. silent mutations:
- mutation does not alter the amino acid sequence of the polypeptide; this is due to the degenerate nature of the genetic code
2. missense mutations:
- alter single amino acid in polypeptide chain
3. nonsense mutations:
- creates a premature stop codon, causing the polypeptide chain produced to be incomplete, thus affecting the final proteins structure and function
64
what does a duplication mutation do
- A whole gene or section of a gene is duplicated so that two copies of the gene/section appear on the same chromosome
- The original version of the gene remains intact and therefore the mutation is not harmful
- Overtime, the second copy can undergo mutations which enable it to develop new functions
65
what does an inversion mutation do
Inversion mutations usually occur during crossing-over in meiosis
- The DNA of a single gene is cut in two places
- The cut portion is inverted 180° then rejoined to the same place within the gene
- results in a large section of the gene which is "backward" and so multiple amino acids are affected, and thus usually a non functional protein
66
what does the presence of the haem group in haemoglobin allow for
1. enables small molecules like oxygen to be bound more easily because as each o2 molecule binds, it alters the quaternary structure of the protein. this allows haemoglobin to have a higher affinity for the subsequent
oxygen molecules and they bind more easily
2. existence of the fe2+ ion in haem group allows o2 to reversibly bind as none of the amino acids that make up the polypeptide chains in haemoglobin are well suited to binding with o2.
67
rna nucleotide structure
- ribose sugar
- phosophate group
- organic base
68
trna structure
- adenine, cytosine, guanine, uracil
- single stranded
- ribose sugar
69
what is the role of tRNA in protein production
- each tRNA brings a specific amino acid to the ribosome
- the tRNA with the complementary anticodon binds to the mRNA codon
70
compare and contrast transcription and DNA replication
similarities:
- involved formation of polynucleotide
- involves DNA helicase unwinding
differences:
- transcription uses RNA nucleotdies, replication uses DNA nucleotides
- transcription produces a single strand, replication produces a double strand
71
explain why plasma membranes are described as having a fluid mosaic structure
- molecules can move within the membrane by diffusion
- the membrane contains both proteins and phospholipids arranged in a pattern
72
state three functions of the phospholipid bilayer
1. forms a partially permeable barrier
2. enables membrane to fuse with other membranes
3. provides fluidity to the membrane
73
explain two differences between facilitated diffusion and active transport
- facilitated diffusion takes place DOWN a conc gradient, whereas at goes against
- facilitated diffusion does not use ATP, at does
74
how has advanced tech taught us more about the cell membrane
- freeze etched electron micrograph showed globular structures scattered through membrane
- improvements in tech used to analyse membrane proteins provided info about size and structure
75
what is the role of cholesterol in the membrane
- prevents phospholipid tails from packing too closely together when the temp decreases in order to maintain membrane fluidity
76
explain 2 features of dna that help stabilise its structure
- h bonds between the base pairs
- many h bonds provide strength
77
what are the advantages for DNA having a double helix
- gives stability to the molecule
- for semi conservative replication
78
what is the importance of the antiparallel nature of DNA
- DNA strands run in opposite directions
- DNA strands have a 3' end and a 5' end
- DNA polymerase can only build the new strand in one direction
79
relate the structure of DNA to its function...
Structure of DNA:
Polymer of nucleotides
Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base
Phosphodiester bonds (between nucleotides)
Double helix/2 strands held by hydrogen bonds
(Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine
Complementary base pairing
Structure related to function:
Polymer/large molecule helps restrict DNA to the nucleus which protects it/base sequence from damage / preserves the genetic code
Strong covalent (phosphodiester) bonds of the backbone help preserve the base sequence
Complementary base pairing keeps equal distance between the two strands to increase the stability of the DNA molecule
Numerous hydrogen bonds help increase stability of the DNA molecule
Weakness of hydrogen bonds means they can be easily broken during replication and transcription
Base pairing means the complementary strand can be replicated
Base sequences act as a store of our genetic information to build proteins
80
explain structural differences between mrna and trna
- mrna is longer
- mrna is a straight molecule, trna is folded
- mrna contains no double stranded sections
81
how does mrna control the process of translation
- contains a start codon that acts as a signal to start translation
- this ensures ribosomes start translation at the correct place
- contains a stop codon to signal the end of translation
82
how does the structure of a globular protein enable it to perform its function
- polar hydrophilic R groups face towards outside enabling it to be soluble
- solubility enables them to perform roles in transport
83
what are the advantages of calculating INITIAL rate of reaction
- A valid comparison can be made between different enzyme activities/reaction rates
- The rate can vary if calculated over a longer period of time
84
what are the names and functions of the enzymes used in DNA replication
- DNA helicase is used to break H bonds
- DNA polymerase is used to join nucleotides together
85
what is the role of free nucleotides
to form a complementary dna strand
86
Two features of DNA and their importance to semi-conservative replication are...
Two strands so both can act as templates
Complementary base pairing so there is accurate replication
87
why was bacteria and nitrogen used to prove semi conservative dna replication
bacteria
- can replicated quickly
- no ethical issues
nitrogen
- Nitrogen is an essential chemical component of DNA / nitrogenous bases
- Therefore every time a cell divides/DNA replicates it incorporates new N atoms into the DNA
88
how does primary structure of a protein enable it to be soluble
primary structure determines the folding of the polypeptide
forming a globular structure
hydrophilic r groups are located on the outside of the protein
water forms h bonds with protein
89
differences between dna and rna
dna is double stranded, rna is single
DNA contains deoxyribose, rna contains ribose
DNA contains thymine, rna contains uracil
90
which of the molecules found in cell membranes have hydrophilic regions
phospholipids, channel proteins and cholesterol
91
Explain why ATP is required for the movement of sodium ions into the cell.
against a concentration gradient
which requires active transport
92
Explain how phospholipids form a cell surface membrane.
hydrophilic parts associate with water
hydrophobic parts repel water
layer forms with hydrophobic parts pointing towards the centre of the cell membrane
93
Explain why the phospholipids are arranged in two layers in a cell surface membrane.
hydrophobic region facing towards water
hydrophilic regions facing away from water
two layers needed as AQUEOUS solution either side of the cell membrane
94
Explain why cystic fibrosis affects the rate of oxygen uptake in the lungs.
- thick mucus
- accumulation of mucus which cannot be moved by cilia
- restricting air flow through bronchi
- reduces surface area for gas exchange in the alveoli
95
Explain why different mutations in the CFTR gene can lead to differences in the severity of the symptoms of cystic fibrosis.
- different mutations will have different effects on the protein produced
- chloride ion transport affected by the extent of changes to the ctfr protein
- varying the thickness of the mucus
96
genetic screening advantages and disadvantages
adult screening:
- identifies risk of developing particular disease in the future so choices can be made
- identification of carriers so choices can be made about family planning
- may not want to know if you have a high chance of developing a disease, potentially affects life insurance
prenatal screening:
- amniocentesis: prepares parents for child with disease/gives choice of abortion
- some of the conditions tested for are very life limiting
- only implant healthy embryos, do not have to make decision regarding abortion
- all pre natal screening has a risk of false positives
- IVF can be unethical as many embryos are discarded
- invasive nature of some of the tests
97
Name the prenatal test that could be used to detect Tay-Sachs disease at 11 weeks of
pregnancy.
- why may someone choose to not have this test
- chorionic villus sampling
- test result may be inaccurate, increased risk of miscarriage, prenatal testing/abortion against values of parents
98
complete vs incomplete vs codominance
In complete dominance, only one allele in the genotype is seen in the phenotype.
In codominance, both alleles in the genotype are seen in the phenotype.
In incomplete dominance, a mixture of the alleles in the genotype is seen in the phenotype.
99
how does CVS work
cells taken from placenta between 10-14 weeks of pregnancy
benefit of earlier diagnosis
risk of miscarriage
100
how does amniocentesis work
Involves testing fetal DNA by taking a sample of amniotic fluid.
This is done by inserting a long, fine needle through the abdomen.
It is carried out during weeks 15-20 of pregnancy and there is a 1% chance of miscarriage as a result of the procedure.
Results are not available until 2-3 weeks after the sample has been taken.
101
State why enzymes are described as biological catalysts.
reduce activation energy of biological reactions
102
Explain how human genome sequencing can be used to identify mutations
sequence genome of people with mutation
sequence genome of people without the mutation
compare base sequences to identify mutations
103
Describe what happens to proteins following the process of translation until they are released from the cell.
- folded in the RER
- packaged into vesicles
- modified in the golgi apparatus
- exocytosis
104
Name the products formed when several amino acids are joined together.
polypeptide and water
