Genes and Health Flashcards
(190 cards)
1
Q
How can you calculate rate of a reaction from a curved line graph
A
tangent then rise over run
2
Q
Why are enzymes highly specific?
A
Enzymes are highly specific due to their tertiary structure. which forms the active site
3
Q
The permeability of cell membranes is affected by:
A
e.g. temperature and alcohol concentration.
4
Q
What does being heterozygous (Ff) mean for cystic fibrosis?
A
The person is a carrier but does not have CF.
5
Q
What is Cystic fibrosis and what is it caused by
A
Cystic fibrosis (CF) is an inherited disorder that mainly affects the respiratory, digestive and reproductive systems . It’s caused by a recessive allele (f), so a person will only have the disorder if they’re homozygous for the allele (ff) — they must inherit one recessive allele from each parent. If a person is heterozygous (Ff), they won’t have CF but they’ll be a carrier.
6
Q
What is the main function of RNA?
A
Transfer genetic information from DNA to ribosomes.
7
Q
Heterozygote
A
An organism that carries two different alleles for a certain characteristic, e.g. Bb
8
Q
What is the shape of DNA?
A
DNA forms a double-helix structure with two antiparallel polynucleotide strands.
9
Q
What does non-overlapping mean in the genetic code?
A
Each base triplet is read separately, without sharing bases with others.
10
Q
What are the four structural levels of proteins?
A
Primary, secondary, tertiary, and quaternary structures.
11
Q
What are the monomers of proteins
A
amino acids
12
Q
What is Duplication
A
One or more bases are repeated, e.g. ATGCCT becomes ATGCCCCT (two Cs are duplicated).
13
Q
Where does the mRNA attach after leaving the nucleus?
A
To a ribosome in the cytoplasm.
14
Q
How are proteins really different
A
different number and order of amino acids. defined by the primary structure which affects the tertiary one
15
Q
What is the key difference between conservative and semi-conservative replication?
A
Conservative keeps original strands together; semi-conservative combines old and new strands.
16
Q
What is the role of CFTR protein and what happens in a mutation?
A
CFTR is a channel protein. It transports chloride ions out of cells and into mucus — this causes water to move into the mucus by osmosis, which makes mucus watery. Mutant CFTR protein is much less efficient at transporting chloride ions out of the cell, so less water moves out by osmosis. This makes the mucus of people with CF abnormally thick and sticky. This thick and sticky mucus causes problems in the respiratory, digestive and reproductive systems.
17
Q
What are proteins made from?
A
Proteins are made from long chains of amino acids. or one or more polypeptides chains
18
Q
What is the difference between facilitated diffusion and active transport?
A
Active transport uses energy to move molecules against a concentration gradient, while facilitated diffusion does not.
19
Q
What is diffusion?
A
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
20
Q
difference between channel and carrier proteins
A
Channel proteins only transport charged particles
carrier proteins transport both
21
Q
What happens during translation
A
amino acids are joined together to
make a polypeptide chain (protein), following the sequence of codons carried by the mRNA.
22
Q
flicks equation what does it mean
A
rate of diffusion ∝ area of diffusion surface × difference in concentration/ thickness of diffusion surface
The ‘proportional to’ bit means that the rate of diffusion will double if:
* the surface area or the difference in concentration doubles, OR
* the thickness of the surface halves.
23
Q
The bonds formed between amino acids are called
A
peptide bonds
24
Q
How is the Reproductive System affected by CF
A
In some men with CF, the tubes connecting the testicles (where sperm are produced) to the penis are absent
and can become blocked by the thick mucus in others. So, any sperm produced can’t reach the penis.
In women, thickened cervical mucus can prevent the sperm from reaching the egg. The sperm has to travel
through this mucus to reach the egg — thick mucus reduces the motility of the sperm, reducing its chances
of making it to the egg.
25
Carrier
If a recessive allele can cause disease, a carrier is someone who has one dominant and one recessive allele
(heterozygous). They won’t have the disease but they carry a copy of the allele for the disease.
26
How long does it take to get results from CVS
Initial results (which tell you whether any obvious major issues have been found) are availablein a few days, but the results of more in-depth and detailed tests can take two weeks or more.
27
draw and describe the structure of DNA mononucleotdie
The pentose sugar in a DNA mononucleotide
is called deoxyribose.
Each DNA mononucleotide has the same sugar and a phosphate group. The base on
each mononucleotide can vary though.
There are four possible bases — adenine (A),
thymine (T), cytosine (C) and guanine (G).
28
What can alter the tertiary structure of an enzyme?
Changes in pH or temperature can alter the tertiary structure of an enzyme.
29
What does cystic fibrosis affect
respiratory, digestive and reproductive systems.
30
Genotype
The alleles a person has, e.g. BB, Bb or bb for eye colour.
31
How You Can Measure How Fast the Product of the Reaction is Made
Catalase catalyses the breakdown of hydrogen peroxide into water and oxygen. It’s easy to measure thevolume of oxygen produced and to work out how fast it’s given off. Using this reaction, you can investigate
the effect of changing the enzyme concentration on the initial rate of reaction — the diagram below showsthe apparatus you’ll need. (You’ll also need a stand and clamp to hold the cylinder upside down, as well as a stopwatch.) During the experiment, the oxygen released displaces the water from the measuring cylinder. You’ll need to decide on a range of catalase concentrations to investigate before you start. Add a set volume and concentration of hydrogen peroxide to a boiling tube. To keep the pH constant, add a set amount of a suitable buffer solution to the tube. (A buffer solution is able to resist changes in pH when small amounts of acid or alkali are added.)
Set up the rest of the apparatus as shown in the diagram. Use a pipette to add a set volume of one of the concentrations of catalase to the boiling tube.
Then quickly attach the bung and delivery tube. Record the volume of oxygen produced in the measuring cylinder every ten seconds for the first minute (60 s) of the reaction. Use a stopwatch to measure the time. Repeat the experiment twice more, and find the average
volume of oxygen produced at each ten second interval. Plot your data on a graph of volume of oxygen produced (cm3) against time (seconds) and draw a tangent (see next page) to determine the initial rate of the reaction. Repeat the whole experiment at each of the other catalase concentrations under investigation. You can then compare the initial rate of the reaction for each
concentration to determine the effect of changing the enzyme concentration on the initial rate of reaction.
32
How does DNa replicate
Semi-Conservative Replication
33
melson and sthal experiment
two samples of bacteria were grown — one in a
nutrient broth containing light nitrogen, and one in a
broth with heavy nitrogen. As the bacteria reproduced,
they took up nitrogen from the broth to help make
nucleotides for new DNA. So the nitrogen gradually
became part of the bacteria’s DNA.
A sample of DNA was taken from each batch of
bacteria, and spun in a centrifuge. The DNA from
the heavy nitrogen bacteria settled lower down the
centrifuge tube than the DNA from the light nitrogen
bacteria — because it’s heavier.
Then the bacteria grown in the heavy nitrogen broth
were taken out and put in a broth containing only light
nitrogen. The bacteria were left for one round of DNA
replication, and then another DNA sample was taken
out and spun in the centrifuge.
If replication was conservative, the original heavy
DNA, which would still be together, would settle at the
bottom and the new light DNA would settle at the top.
If replication was semi-conservative, the new bacterial
DNA molecules would contain one strand of the old
DNA containing heavy nitrogen and one strand of new
DNA containing light nitrogen. So the DNA would
settle out between where the light nitrogen DNA settled
out and where the heavy nitrogen DNA settled out.
As it turned out, the DNA settled out in the middle,
showing that the DNA molecules contained a mixture
of heavy and light nitrogen. The bacterial DNA had
replicated semi-conservatively in the light nitrogen.
34
Explain mRNA
* Made in the nucleus during transcription.
* Three adjacent bases are called a codon.
* It carries the genetic code from the DNA
in the nucleus to the cytoplasm, where it’s
used to make a protein during translation.
35
What happens when there are more enzyme molecules than available substrate?
The more enzyme molecules there are in a solution, the more active sites
are present and therefore the more likely a substrate molecule is to collide
with an active site and form an enzyme-substrate complex. So increasing
the concentration of the enzyme increases the rate of reaction.
But, if the amount of substrate is limited, there comes a point when there’s
more than enough enzyme molecules to deal with all the available substrate,
so adding more enzyme has no further effect. Substrate concentration has
become a limiting factor.
36
What enzyme unwinds DNA during replication?
DNA helicase
37
Carrier proteins function and process
Move large molecules into or
out of the cell, down their concentration gradient. Different carrier proteins facilitate the diffusion of different molecules.
1) First, a large molecule attaches to a
carrier protein in the membrane.
2) Then, the protein changes shape.
3) This releases the molecule on the
opposite side of the membrane.
38
Why is the genetic code described as degenerate?
there are more possible combinations of triplets than there are amino acids (20 amino acids but 64 possible triplets). This means that some amino acids are coded for by more than one base triplet,
39
What isotopes were used in Meselson and Stahl's experiment?
Heavy nitrogen (15N) and light nitrogen (14N).
40
What are peptide bonds?
The bonds formed between amino acids are called peptide bonds.
41
What determines the shape of an enzyme's active site?
The shape of the active site is determined by the enzyme's tertiary structure, which is influenced by its primary structure.
42
Two types of enzymes and what do they do
Enzymes can be intracellular (catalyse reactions inside cells) or extracellular
(produced and secreted by cells to catalyse reactions outside cells).
43
How does gas exchange work in the lungs
Oxygen diffuses out of the alveoli, across the alveolar epithelium (a layer of thin, flat cells) and the capillary endothelium (a type of epithelium that forms the capillary wall), and into the blood. Carbon dioxide diffuses into the alveoli from the blood and is breathed out.
44
What causes cystic fibrosis in the first place
Cystic fibrosis is caused by a mutation in the gene that codes for the CFTR protein (Cystic Fibrosis Transmembrane Conductance Regulator).
45
What does flicks law relate
Fick’s Law relates the rate of diffusion to the concentration gradient, the surface area and the thickness of the
exchange surface. It states that:
46
What is a partially permeable membrane?
A membrane that allows some substances to pass while blocking others.
47
What is the chance of a child having cystic fibrosis if both parents are carriers?
25% chance of the child having cystic fibrosis.
48
What are the social and ethical issues of prenatal testing
- Prenatal tests 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.
49
What is a Gene
A sequence of bases on a DNA molecule that codes for a protein, which results in a characteristic, e.g. the gene for eye colour
50
How are polypeptides formed?
Polypeptides are formed by condensation reactions between amino acids.
51
Who determined the double-helix structure of DNA?
James Watson and Francis Crick determined the structure in 1953.
52
What is chorionic villus sampling (CVS)?
performed around11-14 weeks of pregnancy.
A sample of cells is taken from the chorionic villi (part of the fetus that connects it to its mother). The cells contain fetal DNA, which can be analysed. This procedure is done via either the abdomen (using a fine needle) or the vagina (using a catheter — a thin flexible tube).
53
Incomplete Dominance
When the trait from a dominant allele isn’t completely shown over the trait produced by the recessive allele,
so both alleles influence the phenotype. Some flowers show incomplete dominance,
e.g. snapdragons can have alleles for red flowers (RR), white flowers (rr) or pink flowers (Rr).
54
What is genetic continuity in context of DNA replication
during semi- conservative replication half of the strands in each new DNA molecule are from the original DNA molecule. This means that there’s genetic continuity between generations of cells
55
What is net movement
The overall movement of particles
56
Describe the whole process of transcription
During transcription an mRNA copy of a gene is made in the nucleus:
Transcription starts when RNA polymerase
(an enzyme) attaches to the DNA double-helix
at the beginning of a gene (start codon).
The hydrogen bonds between the two DNA strands
in the gene break, separating the strands, and the
DNA molecule unwinds at that point.
One of the strands is then used as a template
to make an mRNA copy.
The RNA polymerase lines up free RNA mononucleotides
alongside the template strand. Complementary base pairing means
that the mRNA strand ends up being a complementary copy of the
DNA template strand (except the base T is replaced by U in RNA).
Once the RNA mononucleotides have paired up
with their specific bases on the DNA strand
they’re joined together by RNA polymerase,
forming an mRNA molecule.
The RNA polymerase moves along
the DNA, separating the strands and
assembling the mRNA strand.
The hydrogen bonds between the unwound
strands of DNA re‑form once the RNA
polymerase has passed by and the strands
wind back up into a double-helix.
When RNA polymerase reaches a stop codon
(see previous page) it stops making mRNA
and detaches from the DNA.
The mRNA moves out of the nucleus through
a nuclear pore and attaches to a ribosome in
the cytoplasm, where the next stage of protein
synthesis takes place
57
What are mutations and what do they do
Mutations are changes to the base sequence of DNA during replication. They can be caused by errors during DNA replication
58
What is a polynucleotide
its a polymer of mononucleotides.
Both DNA and RNA mononucleotides form
polynucleotides.
59
What is an active site?
The specific part of an enzyme where substrate molecules bind.
60
What is a gene?
A sequence of mononucleotide bases on a DNA molecule that codes for amino acids in a polypeptide.
61
What did Meselson and Stahl's experiment provide evidence for?
Semi-conservative replication of DNA.
62
what is The phospholipid bilayer described as
'fluid mosaic'
The scattered pattern produced by the components within the phospholipid bilayer looks some what like a mosaic when viewed from above The mosaic of phospholipids and proteins can move around within the bilayer by diffusion, hence the mosaic is said to be 'fluid' The phospholipids mainly move sideways, within their own layer
The many different types of proteins interspersed through out the bilayer move about within it, although some may be fixed in position
63
cholesterol function in the membrane
Cholesterol can be found between the phospholipids, where it regulates membrane fluidity
Cholesterol increases the fluidity of the membrane at low temperatures, stopping it from becoming too rigid This occurs because cholesterol stops the phospholipid tails packing too closely together
Interaction between cholesterol and phospholipid tails also stabilises the cell membrane at higher temperatures by stopping the membrane from becoming too fluid
Cholesterol increases the mechanical strength and stability of membranes; without it membranes would break down and cells would burst
64
What cell membranes do
The cell surface membrane creates an enclosed space separating the internal cell environment from the external environment,
Membranes do not only separate different areas but also control the exchange of substances from one side of a membrane to the other, as well as acting as an interface for communication
65
What are the two types of prenatal tests?
Amniocentesis and chorionic villus sampling.
66
what do Genetic diagrams do
can be used to predict the genotypes and phenotypes of the offspring produced if two parents are crossed (bred).You need to be able to interpret genetic diagrams for characteristics
67
What are some social and ethical issues of carrier testing?
Emotional stress(knowing your a carrier), false results, discovery of other genetic abnormalities, and potential genetic discrimination.
68
What is released during the formation of polypeptides?
A molecule of water
69
similarity between endocytosis and exocytosis
They both require ATP
70
What are start and stop codons?
triplets are used to Signal the beginning and end of protein production. and found at the beginning and at the end of the gene
71
What is Inversion
a sequence of bases is reversed, e.g. ATGCCT becomes ATGTCC (CCT is reversed).
72
What happens if a mutation occurs in a gene?
it can cause a genetic disorder, which is then passed on.
E.g. cystic fibrosis (CF) is a genetic disorder caused by a mutation in a gene. The protein the gene codes for is important for mucus production
73
What do ribosomes do?
Ribosomes are the body’s
‘protein factories’ — they read the RNA to make polypeptides (proteins) in a process called translation. Ribosomes themselves are made from RNA and proteins.
74
What is the risk of miscarriage with CVS?
1-2%, which is greater than with amniocentesis.
75
Homozygote
An organism that carries two copies of the same allele for a certain characteristic, e.g. BB or bb.
76
Exocytosis function and process
Some substances produced by the cell (e.g. digestive enzymes, hormones, lipids) need to
be released from the cell — this is done by exocytosis.
Vesicles containing these substances pinch off from the 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.
Some substances (like membrane proteins) aren’t released outside the cell — instead they are inserted straight into the cell membrane.
Exocytosis uses ATP as an energy source.
77
What happens if a mutation occurs in a gene? in terms of structure
It can alter the primary structure of the protein it codes for. This could change the final 3D shape of the protein so it doesn’t work properly like the tertiary structure
78
What is genetic screening?
Process of analysing DNA to see if it contains alleles for genetic disorders.
79
Draw an amino acid
book
80
What is Deletion
one base is deleted, e.g. ATGCCT becomes ATCCT (G is deleted).
81
Whole process of translation
The mRNA attaches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to the ribosome.
A tRNA molecule, with an anticodon that’s complementary to the start codon on the
mRNA, attaches itself to the mRNA by complementary base pairing.
A second tRNA molecule attaches itself to the next codon on the mRNA in the same way.
The two amino acids attached to the tRNA molecules are then joined together by a
peptide bond. The first tRNA molecule moves away, leaving its amino acid behind.
The ribosome moves along to the next codon.
A third tRNA molecule binds to that codon on the mRNA.
Its amino acid binds to the first two and the second tRNA molecule moves away.
This process continues, producing a chain of linked amino acids (a polypeptide chain),
until there’s a stop codon on the mRNA molecule.
The polypeptide chain moves away from the ribosome and translation is complete.
82
What is the role of enzymes in metabolic reactions?
Enzymes catalyse metabolic reactions at both cellular and organism levels.
83
What bonds are formed in each structure in protiens
Primary structure — held together by the peptide bonds between amino acids.
Secondary structure — held together by hydrogen bonds (see previous page).
Tertiary structure — this is affected by a few different kinds of bonds:
* Ionic bonds. These are attractions between negative atom in another molecule.
and positive charges on different parts of the molecule.
* Disulfide bonds. Whenever two molecules of the amino acid cysteine come close together, the sulfur atom in one cysteine bonds to the sulfur in the other cysteine, forming a disulfide bond.
* Hydrophobic and hydrophilic interactions. When hydrophobic (water-repelling) groups are close together in the protein, they tend to clump together. This means that hydrophilic (water-attracting) groups are more likely to be pushed to the outside, which affects how the protein folds up into its final structure.
* Hydrogen bonds.
Quaternary structure — this tends to be determined by the tertiary structure of the individual polypeptide chains being bonded together. Because of this, it can be influenced by all the bonds mentioned above.
84
Recessive
An allele whose characteristic only appears in the phenotype if two copies are present, e.g. the allele for blue eyes (b) is recessive — if a person’s genotype is bb, they’ll have blue eyes. Recessive alleles are shown by a lower case letter.
85
What are advantages of PGD?
The advantages of PGD are that it reduces the chance of having a baby with a genetic disorder — only embryos without the genetic disorders tested for will be implanted. Also, because it’s performed before implantation, it avoids the issue of abortion
86
Why is mucus necessary
it helps prevent lung infections by trapping microorganisms. The mucus (with the microorganisms) is transported towards the throat by cilia (small hair-like structures that beat to move mucus along).
87
Are membranes permeable? and what can pass
Membranes are partially permeable
Substances can cross membranes by diffusion and active transport
Small, non-polar molecules can pass through the gaps between the phospholipids
Large, polar molecules must pass through specialised membrane proteins called channel proteins and carrier proteins
88
channel proteins function
Channel proteins form pores in the
membrane for charged particles to diffuse
through (down their concentration gradient).
Different channel proteins facilitate the
diffusion of different charged particles.
89
How are the Lungs are Adapted for Efficient Gaseous Exchange
Having lots of alveoli means there is a large surface area for diffusion to occur across.
The alveolar epithelium and capillary endothelium are each only one cell thick, giving a short diffusion pathway.
All the alveoli have a good blood supply from capillaries — they constantly take
away oxygen and bring more carbon dioxide, maintaining the concentration gradient.
Breathing in and out refreshes the air in the alveoli, keeping the concentration gradients high.
90
How do enzymes affect activation energy?
Enzymes lower the activation energy required for a reaction, allowing it to occur at lower temperatures.
91
What are mononucleotides and what are they made of
A mononucleotide is a type of biological molecule they’re the monomers that make up DNA and RNA.
* a pentose sugar (that’s a sugar with 5 carbon atoms),
* a nitrogen-containing organic base,
* a phosphate group.
92
What did Meselson and Stahl’s want to find out
whether DNA replication was semi-conservative or conservative.
93
Where does transcription occur?
In the nucleus
94
Who is offered prenatal tests?
Pregnant women with a family history of genetic disease.
95
What is DNA made of
two polynucleotide strands joined together by hydrogen bonds between the bases
96
What is prenatal testing
Prenatal tests involve screening unborn babies (fetuses) for genetic disorders.
97
what happens if phospholipids are spread over water
form a single layer with the hydrophilic
phosphate heads in the water and the hydrophobic fatty acid tails sticking up away from the water This is called a phospholipid monolayer
98
How is a genetic pedigree diagram structured?
Parents are joined by a horizontal line; children are connected by vertical lines.
99
What is Substitution
one base is substituted with another, e.g. ATGCCT becomes ATTCCT (G is swapped for T).
100
How do two DNA polynucleotide strands join together?
They join by hydrogen bonding between the bases.
101
Why do people with cystic fibrosis have thick mucus?
Due to a genetic defect affecting chloride channels, leading to abnormal mucus production.
102
What is complementary base pairing?
Each base pairs with one specific partner: A with T, C with G.
103
What are DNA and RNA?
Nucleic acids and carry information
104
What determines the primary structure of a protein? and how could this be a problem
The primary structure (amino acid sequence) of a protein is determined by a gene.
If a mutation occurs in that gene it could change the tertiary structure of the enzyme produced.
105
Why is the lock and key model incorrect
The enzyme and substrate do
have to fit together in the first place, but new evidence showed that the enzyme-substrate complex changed shape slightly to complete the fit. This locks the substrate even more tightly to the enzyme. Scientists modified
the old lock and key model and came up with the ‘induced fit’ model.
106
Are enzymes specific?
they usually only catalyse one reaction, e.g. maltase only breaks down maltose, sucrase only breaks down sucrose.
107
What does RNA polymerase do during transcription?
It separates DNA strands and assembles the mRNA strand.
108
How does substrate concentration affect reaction rate?
The higher the substrate concentration, the faster the reaction — more
substrate molecules means a collision between substrate and enzyme is
more likely and so more active sites will be used. This is only true up until a
‘saturation’ point though. After that, there are so many substrate molecules
that the enzymes have about as much as they can cope with
(all the active sites are full), and adding more makes no difference.
Substrate concentration decreases with time during a reaction (unless more
substrate is added to the reaction mixture), so if no other variables are
changed, the rate of reaction will decrease over time too. This makes the
initial rate of reaction (the reaction rate at the start) the highest rate of reaction.
109
How can you investigate the permeability of the cell membrane
Beetroot cells contain a coloured pigment that leaks out — the higher the permeability of the membrane, the more pigment leaks out of the cell.
Use a scalpel to carefully cut five equal sized pieces of beetroot. (Make sure you do your
cutting on a cutting board.) Rinse the pieces to remove any pigment released during cutting.
Use a measuring cylinder or pipette to measure 5 cm3 of water into five different test tubes.
Place the test tubes into water baths at different temperatures, e.g. 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, for around 5 minutes to allow the water to reach the desired temperature.
Place the five pieces of beetroot into the five different test tubes, for the same length of time
(measured using a stopwatch).
Remove the pieces of beetroot from the tubes, leaving just the coloured liquid.
Firstly, switch the colorimeter on and allow five minutes for it to stabilise.
Then set up the colorimeter so you’re using a blue filter (or a wavelength of
about 470 nm) and use pure water to calibrate the machine to zero.
Next, use a pipette to transfer a sample of the liquid from the first of your
beetroot test tubes to a clean cuvette — it should be about three quarters full.
Put the cuvette in the colorimeter and record the
absorbance of the coloured solution.
Repeat steps 2-3 for the liquids in the remaining four test tubes
(using a clean pipette and cuvette each time).
You’re now ready to analyse your results — the higher the absorbance
reading, the less light is passing through the solution. This means more
pigment has been released, so the higher the permeability of the membrane.
110
What is osmosis?
The diffusion of free water molecules across a partially permeable membrane from higher to lower concentration of water molecules.
111
What is a dipeptide?
A dipeptide is formed when two amino acids join together.
112
What are the types of erros that can occur during mutation
Substitution, Deletion, Insertion, Duplication, Inversion
113
What is the genetic code?
Sequence of base triplets (codons) in DNA or mRNA coding for amino acids.
114
What is a colorimeter
a machine that passes light of a specific wavelength through a liquid and measures how much of that light is absorbed. Many colorimeters use filters to make sure the light passing through the liquid is at the desired wavelength.
115
What happens to the hydrogen bonds after RNA polymerase passes?
They re-form, and the DNA strands wind back into a double-helix.
116
What is the induced fit model
The ‘induced fit’ model helps to explain why enzymes are so specific and only bond to one particular substrate.
The substrate doesn’t only have to be the right shape to fit the active site, it has to make the active site change shape
in the right way as well. This is a prime example of how a widely accepted theory can change when new evidence
comes along. The ‘induced fit’ model is still widely accepted — for now, anyway
117
Advantages of carrier testing
allows people to make informed decisions about things like whether to have children after determining the chances of any future children having the disorder and whether to carry out prenatal testing if the woman is pregnant
118
What does DNA store?
Genetic information for growth and development.
119
What is the first stage of protein synthesis?
Transcription
120
What happens to DNA before cell division and why
DNA copies itself so that each new cell has the full amount of DNA.
121
What is the relationship between surface area and volume ratios in organisms?
Large objects have smaller surface area to volume ratios than small objects, affecting gas exchange efficiency.
122
How are the two strands of DNA oriented?
The two strands are antiparallel, running in opposite directions.
123
What is a catalyst?
A substance that speeds up a chemical reaction without being consumed in the process.
124
What is the gas exchange surface in mammals
The alveolar epithelium in the lungs
125
What role does mucus have in the digestive, reproductive and respiratory
Mucus is also secreted by the reproductive system — it helps to prevent infections and transport sex cells
(sperm or eggs).
Everyone also has mucus in their digestive system. its protection from excess stomach acid and acts as a lubricant
it helps prevent lung infections by trapping microorganisms. The mucus (with the microorganisms) is transported towards the throat by cilia (small hair-like structures that beat to move mucus along
126
What is amniocentesis?
This is usually carried out at 15-20 weeks of pregnancy.
A sample of amniotic fluid (the fluid that surrounds the fetus)is obtained via the abdomen using a very fine needle. This fluid contains fetal cells. The cells contain DNA, which can be analysed.
127
What are the bonds in sugar-phosphate backbone?
phosphodiester between the phosphate group of one nucleotide to the deoxyribose creating the sugar-phosphate backbone
and hydrogen bonds between AT. CG
128
What determines the order of amino acids in a protein?
The order of mononucleotide bases in a gene.
129
Describe semi-conservative replication
The enzyme DNA helicase
breaks the hydrogen bonds
between bases on the two
polynucleotide DNA strands.
This makes the helix unwind
to form two single strands.
Each original single strand acts
as a template for a new strand.
Complementary base pairing
means that free-floating DNA
nucleotides are attracted to their
complementary exposed bases
on each original template strand
— A with T and C with G.
Condensation reactions join the
nucleotides of the new strands together —
catalysed by the enzyme DNA polymerase.
Hydrogen bonds form between the bases
on the original and new strands.
Each new DNA molecule contains
one strand from the original DNA
molecule and one new strand.
130
Explain Transfer RNA (tRNA)
Found in the cytoplasm.
* It has an amino acid
binding site at one end
Anticodon
and a sequence of three
bases at the other end
called an anticodon.
* It carries the amino acids that are used to make
proteins to the ribosomes during translation.
131
Is diffusion a passive process?
Yes, diffusion is a passive process that requires no energy.
132
What is concentration gradient
The path from an area of higher concentration to an area of lower concentration. Particles diffuse down a concentration gradient.
133
What can cause genetic disorders?
Having too few or too many chromosomes, or mutations in genes.
134
What is Insertion
An extra base is added, e.g. ATGCCT becomes ATGACCT (an extra A is added).
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How does a proteins primary structure determine its 3ds structure and properties
The amino acid sequence of a protein determines what bonds will form and how the protein will fold up into its 3D structure. E.g. if there are many cysteines, these will form disulfide bonds with each other, so the protein folds up in a certain way. The 3D structure of a protein determines its properties. Its properties relate to its function in the body.
136
What does a key in a genetic pedigree diagram represent?
It shows what the shapes represent, such as unaffected or affected individuals.
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What is the ‘Lock and Key’ Model
This is where the substrate fits into the enzyme in the same way that a key fits into a lock.
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What type of sugar is in RNA?
Ribose
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How many hydrogen bonds form between C and G?
Three hydrogen bonds form between cytosine and guanine (C - G).
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What are the three main uses of genetic screening?
1. Identification of carriers 2. Preimplantation Genetic Diagnosis (PGD) 3. Prenatal testing
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Glycolipids and glycoproteins function in the membrane and structure
They are present on the surface of the cell, where they aid cell-to-cell communication
Glycoproteins are proteins with carbohydrate attached, while glycolipids are lipids with
carbohydrate attached
they bind with substances at the cell’s surface, e.g. hormones
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Dominant
An allele whose characteristic appears in the phenotype even when there’s only one copy, e.g. the allele for brown
eyes (B) is dominant — if a person’s genotype is Bb or BB, they’ll have brown eyes. Dominant alleles are
shown by a capital letter.
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What are globular proteins
Globular proteins are round, compact proteins made up of multiple polypeptide chains.
The chains are coiled up so that hydrophilic (water-attracting) parts of chains are on the
outside of the molecule and hydrophobic (water-repelling) parts of chains face inwards.
This makes the proteins soluble, so they’re easily transported in fluids.
E.g. haemoglobin is a globular protein made of four polypeptide chains. It carries
oxygen around the body in the blood. It’s soluble, so it can be easily transported
in the blood. It also has iron-containing haem groups that bind to oxygen.
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What happens if the substrate shape doesn't match the active site? and why
Each different enzyme has a different tertiary structure and so a different shaped active site.If the substrate shape doesn’t match the active site, an enzyme-substrate complex won’t be formed and the reaction won’t be catalysed.
145
What is Preimplantation Genetic Diagnosis (PGD)?
carried out on embryos produced by in vitro fertilisation (IVF). It involves screening embryos for genetic disorders before they’re implanted into the woman.
146
What is the advantage of CVS over amniocentesis?
CVS can be performed earlier, allowing for earlier decisions regarding pregnancy.
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active transport process
a molecule attaches to the
carrier protein, the protein changes shape
and this moves the molecule across the
membrane, releasing it on the other side. (from low to high concentration)
The only difference is that energy is used
— this energy comes from ATP.
* ATP is produced by respiration.
* It acts as an immediate source of
energy in the cell.
* When ATP is hydrolysed (broken
down) in the cell, energy is released.
This energy is used to move the molecule
against its concentration gradient.
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What are the two ways to measure rate of reaction
How Fast the Product of the Reaction is Made
Measure How Fast the Substrate is Removed
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Phenotype
The characteristics displayed by an organism, e.g. brown eyes.
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What is Monohybrid inheritance
its the inheritance of a single characteristic controlled by different alleles.
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What is a polypeptide?
A polypeptide is formed when more than two amino acids join together.
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Proteins function in the membrane
Proteins are involved with cell transport and communication
The proteins can either be intrinsic or extrinsic
Intrinsic proteins can also be referred to as integral
Extrinsic proteins can also be referred to as peripheral
Intrinsic proteins are embedded in the membrane with their precise arrangement determined by their hydrophilic and hydrophobic regions
Extrinsic proteins are found on the outer or inner surface of the membrane
153
What is the genetic code
sequence of base triplets (codons) in DNA or mRNA,
which codes for specific amino acids.
154
How is the respiratory system affected by CF
The cilia are unable to move the mucus towards the throat because it’s so thick and sticky.
This means the mucus builds up in the airways.
Some airways can become completely blocked by the mucus — gas exchange can’t take place in the area below the blockage.This means that the surface area available for gas exchange is reduced, causing breathing difficulties.
People with CF are also more prone to lung infections as mucus-containing microorganisms can’t be removed.
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Most gas exchange surfaces have two things in common
1)They give gas exchange organs (like the lungs) a large surface area to volume ratio
2) They’re thin (often just one layer of epithelial cells) — this provides
a short diffusion pathway across the gas exchange surface.
The organism also maintains a steep concentration gradient of gases across the exchange surface. these all increase the rate of diffusion
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What can prenatal testing allow parents to do?
Make informed decisions about the pregnancy and future care of the child. either abortion or keep and could also start preparing healthcare for the child
157
What are enzymes made of?
proteins
158
How are mononucleotides joined together
through condensation reactions between the phosphate of one mononucleotide
and the sugar group of another. As in all condensation reactions, water is a by-product
159
Is active transport active or passive process
active it requires energy, energy is used
— this energy comes from ATP.
* ATP is produced by respiration.
* It acts as an immediate source of
energy in the cell.
* When ATP is hydrolysed (broken
down) in the cell, energy is released.
This energy is used to move the molecule
against its concentration gradient
160
What are amino acids coded by
by a sequence of three bases (called a triplet) in a gene.
161
What enzyme initiates transcription?
RNA polymerase
162
How is the Digestive system affected by CF
The tube that connects the pancreas to the small intestine can become blocked with mucus — preventing digestive enzymes produced by the pancreas from reaching the small intestine. This reduces the ability of someone with CF to digest food and so fewer nutrients can be absorbed.
The mucus can cause cysts (growths) to form in the pancreas. These inhibit the production of enzymes, which also reduces the ability to digest food and absorb nutrients. The mucus lining the small intestine is abnormally thick — this inhibits the absorption of nutrients.
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What are cell membranes made up of in detail
bilayer, of phospholipids
Phospholipids consist of
A molecule of glycerol
A phosphate group, which forms the phosphate head
Two fatty acid tails, making up the lipid tail
Phospholipids contain two distinct regions: a polar head and two non-polartails
The phosphate head of a phospholipid is polar, meaning thatit can interact with polar water molecules; the head is therefore described as being hydrophilic
The lipid tail is non-polar, meaning thatit cannotinteract with polar molecules;the tail is therefore described as hydrophobic
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Describe 4 structural levels of a protein
Primary Structure — The Dna of a cell decides the structure or the protein by adding specific amino acids in in specific quantities in specific order the sequence of amino acids joined by covalent peptide bonds
.
Secondary Structure — the polypeptide chain doesn’t remain flat and straight.
Hydrogen bonds form between the amino acids in the chain.
This makes it automatically coil into an alpha (a) helix or fold into a
beta (b) pleated sheet — this is the secondary structure.
Tertiary Structure — the coiled or folded chain of amino acids is often
coiled and folded further. More bonds form between different parts of the
polypeptide chain, including hydrogen bonds and ionic bonds (see next page).
Disulfide bonds can also form (see next page). For proteins made from a
single polypeptide chain, the tertiary structure forms their final 3D structure.
Quaternary Structure — some proteins are made of several different
polypeptide chains held together by bonds. The quaternary structure is
the way these polypeptide chains are assembled together. For proteins
made from more than one polypeptide chain (e.g. haemoglobin, insulin,
collagen), the quaternary structure is the protein’s final 3D structure.
Ionic bonds. These are attractions between negative
atom in another molecule.
and positive charges on different parts of the molecule.
* Disulfide bonds. Whenever two molecules of the amino acid cysteine come close together, the sulfur atom in one cysteine bonds to the sulfur in the other cysteine, forming a disulfide bond.
* Hydrophobic and hydrophilic interactions. When hydrophobic (water-repelling) groups are close together in the protein, they tend to clump together. This means that hydrophilic (water-attracting) groups are more likely to be pushed to the outside, which affects how the protein folds up into its final structure.
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What is facilitated diffusion?
It is the process where larger molecules(amino acids and glucose) and charged particles diffuse through carrier or channel proteins in the cell membrane.
166
What is carrier testing and who is it given to
It shows whether people without a disorder carry an allele that can cause a disorder, like CF. Testing offered to individuals with a family history of genetic disorders to see if they carry alleles for those disorders.
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What is an Allele
A different version of a gene. Most plants and animals, including humans, have two copies of each gene, one
from each parent. The two copies can be the same or they can be different. Different versions (alleles) have
slightly different base sequences, which code for different versions of the same characteristic, e.g. brown eyes and
blue eyes. They’re represented using letters, e.g. the allele for brown eyes (B) and the allele for blue eyes (b).
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What are the two types of RNa
Messenger RNA (mRNA)
Transfer RNA (tRNA)
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What is active transport
Active transport uses energy to move molecules and ions across plasma membranes, against a concentration gradient. This process involves carrier proteins.
170
What forms when a substrate fits into an enzyme's active site?
An enzyme-substrate complex is formed.
171
What type of sugar is in DNA?
Deoxyribose.
172
Why is CVS better than amniocentesis physically
Because it can take place earlier in a pregnancy than amniocentesis, an earlier decision to abort can be made, meaning that the procedure is less physically traumatic.
173
What is activation energy?
The energy needed to start a chemical reaction, often supplied as heat.
174
What is the role of complementary base pairing in DNA replication?
Free-floating nucleotides match with exposed bases
175
How long does it take to get results from amniocentesis?
Results aren’t available until 2-3 weeks after the sample is taken, although a rapid test (which only looks for a few of the most common disorders) can also be performed. The results of the rapid test are usually available in 3-4 days
176
How many hydrogen bonds form between A and T?
Two hydrogen bonds form between adenine and thymine (A - T).
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Endocytosis function and process
Some molecules are way too large to be taken into a cell by carrier proteins, e.g. proteins, lipids and some carbohydrates.
Instead a cell 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 is endocytosis.
Some cells also take in much larger objects by endocytosis — for example, some white blood cells (called phagocytes) use
endocytosis to take in things like microorganisms and dead cells so that they can destroy them. Like active transport, (see previous page), this process also uses ATP for energy.
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What is the % of miscarriage in amnioentesis
1%
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how is DNA is Copied into RNA for Protein Synthesis
DNA molecules are found in the nucleus
of the cell, but the organelles that make
proteins (ribosomes)
are found in the cytoplasm.
DNA is too large to move out of the
nucleus, so a section is copied into
mRNA . This process is
called transcription .
The mRNA leaves the nucleus and joins with
a ribosome in the cytoplasm, where it can
be used to synthesise a protein. This process
is called translation
180
What is Second Stage of Protein Synthesis
Translation
181
PGD social and ethical issues
It can be used to find out other characteristics (e.g. gender, eye colour) — leading to concerns that in the future, embryos may be selected for other characteristics (designer babies).
* False results could provide incorrect information.
182
draw and describe the structure of RNA mononucleotide
RNA contains mononucleotides with a ribose sugar
Like DNA, an RNA mononucleotide
also has a phosphate group and
one of four different bases.
In RNA though, uracil (U) replaces thymine as a base.
A-U. C-G
183
How do water molecules move through a cell membrane?
Water molecules diffuse both ways, but net movement is towards lower concentration of water molecules.
184
When does diffusion stop
Until dynamic equilibrium is reached
185
What happens if the tertiary structure of an enzyme is altered
the shape of the active site will change.
This means the substrate won’t fit into the active site, an enzyme-substrate complex won’t be formed and the enzyme will no longer be able to carry out its function
186
Is facilitated diffusion an active or passive process?
It is a passive process that does not use energy.
187
How many mutations can cause cystic fibrosis?
Over 1000 possible mutations are known to cause CF.
188
Why do enzyme-substrate complex lower activation energy
If two substrate molecules need to be
joined, being attached to the enzyme
holds them close together, reducing any
repulsion between the molecules so they
can bond more easily.
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.
189
What are the four bases in DNA?
Adenine (A), thymine (T), cytosine (C), guanine (G).
190
what are fibrous proteins
Fibrous proteins are made up of long, insoluble polypeptide chains
that are tightly coiled round each other to form a rope shape.
The chains are held together by lots of bonds (e.g. disulfide
and hydrogen bonds), which make the proteins strong.
Because they’re strong, fibrous proteins are often found in supportive tissue.
E.g. collagen is a strong, fibrous protein that forms connective tissue in animals.
