1
Q
What happens when you inhale?
A
- Intercostal muscles contract to lift the ribs up and outwards
- The diaphragm muscles contract to flatten the diaphragm
- This creates a larger volume inside the lungs so that pressure decreases
- Air is drawn into the lungs along the pressure gradient
2
Q
What happens when you exhale?
A
- Intercostal muscles relax so the ribcage drops down and inwards
- The diaphragm muscles relax and move upwards
- This creates a smaller volume in the lungs and so pressure increases
- The increased pressure forces the air out of the lungs
3
Q
What is the rate of gas exchange affected by?
A
- The surface area available for diffusion
- Length of diffusion pathway
- Conc. gradient across gas exchange surfaces
- The speed of molecules diffusing through membrane, which is affected by;
- Mass of the molecule
- Permeability of membrane
- Temperature and pressure of the molecule
4
Q
What must efficient gas exchange systems have?
A
- Have a large SA:V ratio (circular alveoli)
- Be thin (lung walls)
- Be able to keep a steep conc. gradient (blood and capillaries)
- Be permeable to gases
5
Q
What is the structure and function of Alveoli?
A
- Moist surface = oxygen dissolves and diffuses through wall into capillary
- Thin walls = small diffusion pathway, squamous epithelium
- Capillary walls = small interstices where O2 pass into blood
- Spherical = large SA:V
- Pulmonary Surfactant = lowers tension of mucus to allow gases to diffuse in and out
- Capillaries cover each alveoli = O2 and CO2 can diffuse in/out of blood plasma
- Squamous = covered w/ characterised by scales
- Squamous epithelial cells are thin and disc shaped like scales
6
Q
What is the equation for Fick’s Law?
A
Rate of diffusion ά SA x Dif in Conc.
————————————————-
thickness of gas exchange surface
ά = directly proportional to
7
Q
What is the structure of Amino Acids?
A
- Check diagram
8
Q
What are condensation reactions?
A
- Condensation reactions form peptide bonds, hydrolysis breaks them
- A condensation reaction joins two amino acids together to form a dipeptide and H2O
9
Q
What is the primary protein structure?
A
- Primary structure = linear amino acid sequence of the polypeptide chain
- Determined by the DNA sequence of the gene coding for a protein
- Peptide bonds (PP)
10
Q
What is the secondary protein structure?
A
- Secondary Structure = folding of the protein chain, eg. into an alpha helix
- Hydrogen bonds (SH)
11
Q
What is the tertiary protein structure?
A
- Tertiary Structure = further folding and attractions b/w alpha helices or beta pleated sheets to give a specific 3D shape, eg. enzymes (one polypeptide chain)
- Di-sulfide bridges (TD)
12
Q
What is the quaternary protein structure?
A
- Quaternary Structure = a protein that consists of more than one polypeptide chain
- Eg. Haemoglobin consists of 4 polypeptide chains
- Ionic, covalent or hydrogen bonds (QHIC)
13
Q
What is the original Primary structure = 3D structure in Tertiary structure
A
- The order and number of amino acids (and their R group) means hydrogen bonds will form in different places
- Hydrogen bonds forming in different place means different secondary structures
- More bonding dependent on its amino acids = tertiary structure
14
Q
What are globular proteins?
A
- Globular proteins = ball-like proteins where hydrophobic parts are towards the centre, and the hydrophilic parts are towards the edges
- Are water soluble b/c of placement of hydrophobic/philic parts
- Eg. enzyme and antibodies
15
Q
What are fibrous proteins?
A
- Fibrous proteins = proteins formed from long fibres, and consist mostly of repeated amino acid sequences
- Insoluble in water and used in structural roles
- Eg. collagen in bones and keratin in nails and hair
16
Q
What are integral proteins?
A
- Channel proteins = allow the transport of specific substances across a membrane
- Facilitated diffusion and passive transport
- Polar molecules, such as, water and sugars
- Carrier Proteins = make diffusion across a membrane easier
- Active transport
- Charged particles, such as, ions
17
Q
What are phospholipids?
A
- Structure = two fatty acid tails joined together by a glycerol molecule
- Properties = head is polar/ hydrophilic, two fatty acid tails are non polar/ hydrophobic
- Are arranged into a bilayer
- Hydrophilic head arranges itself so it’s directly exposed to water molecules
- Hydrophobic tail isolates itself from water, does by having the hydrophilic heads on either side of them
- Non polar molecules that can diffuse through:
O2 and CO2
18
Q
What is the fluid mosaic model?
A
Fluid = molecules are free to move about
Mosaic = proteins are randomly distributed
Differences inc.
Proteins are intrinsic
Some proteins are extrinsic, and are attached to a sugar or lipid chain
Cholesterol is present
Molecules are free to move
19
Q
What is the structure of the fluid mosaic model?
A
- Glycoprotein = proteins w/ a sugar attached covalently to polypeptide chain
- Glyco-lipid = lipids w/ a carbohydrate attached by a glycosidic bond
- Maintain stability of the membrane
- Facilitate cellular recognition
- Peripheral proteins = adhere temporarily to the biological membrane, w/ hydrogen bonds
- Extrinsic proteins = loosely attached by ionic bonds or calcium bridges to the electrically charged phosphoryl surface of the membrane
- Serve in transport of molecules as receptors
20
Q
What is osmosis?
A
- Osmosis = the facilitated diffusion of water from an area of high free water conc. to an area of low free water conc. via channel proteins
- High free water = high water potential, eg. pure water = 0ψ
- Low free water = low water potential, eg. concentrated solution = -120ψ
- The more -ve the water potential the more concentrated the solution
21
Q
What is Active Transport?
A
- Against a conc. gradient (low -> high)
- Requires ATP energy to make carrier proteins change shape (aerobic respiration)
- Carrier proteins needed
22
Q
What is facilitated diffusion?
A
- With a conc. gradient (high -> low)
- Passive transport (doesn’t require energy)
- Uses channel proteins
23
Q
What is simple diffusion?
A
- Same as facilitated, except no proteins
24
Q
What is Endocytosis?
A
- Bulk transport into a cell (large volume of molecules)
- ATP energy used in the movement of vesicles in through the plasma membrane
25
What is exocytosis?
- Bulk transport out of a cell
- ATP energy used in the movement of the vesicle out through the plasma membrane
26
What is the function of the lungs without CF?
* When mucus is wet
- Na+ pump produces a high conc. of Na+ ions outside the cell at the basal end
- By actively transporting Na+ ions out of the cell (Channel proteins)
- Na+ ions diffuse in to replace those pumped out, which lowers the ψ of mucus (facilitated diffusion via channel proteins)
- Water is lost b/c osmosis, which draws water out of the mucus at the apical end in response
* When mucus is dehydrated
- The CFTR channel opens, so Cl- ions diffuse out (facilitated diffusion)
- The CFTR channel stops the Na+ channel from allowing Na+ ions to enter
- Cl- and Na+ ions build up in the mucus and reverse the direction of osmosis
- More water enters mucus reducing viscosity
27
What are the effects of CF on the respiratory system?
- Cilia are unable to move the mucus b/c its too thick
- Mucus builds up in airways
- Airways become blocked
- Lung infections may occur b/c the mucus contains bacteria
28
What is CF?
- The CFTR protein is absent or doesn’t function properly
- w/o it there is no Cl- ions leaving the cell and no regulation of the Na+ channel
- Ψ inside cell cytoplasm remains more -ve than ψ in the mucus
- The direction of osmosis can’t be reversed in response to dehydrated mucus
29
What are the effects of CF on the reproductive system?
- Pancreatic duct becomes blocked w/ mucus
- Digestive enzymes can’t reach small intestine
- Mucus lining the small intestine is thick
- Malnutrition may occur b/c can’t absorb nutrients in food
30
What are the effects of CF on the digestive system?
- In men, sperm are prevented from reaching the penis
- In women, cervical mucus is thick preventing sperm reaching the egg
31
What is the enzyme structure?
- Proteins in enzymes are globular, and in their secondary and tertiary structure
- Many consist of a protein and a non-protein (called the cofactor)
- Have intra and intermolecular bonds, which are affected by pH and temperature
32
How do enzymes function? (Lock and Key)
- Lock-and-key hypothesis
- States that shape of active site and substrate are the same
- When a substrate collides w/ same shape active site it will fit together and form enzyme-substrate complex
- Enzyme will catalyse the reaction
- The products and enzyme will form an enzyme-product complex
- Model suggests that enzymes can catalyse reverse reactions
33
How do enzymes function? (Induced Fit)
- States active sites are not exactly complimentary
- Change shape when near a specific substrate to fit it
- When a substrate collides w/ an enzyme, if its composition is specifically correct the shape of the active site will change
- Substrate then fits and forms enzyme-substrate complex
- Reaction is then catalysed and enzyme-product complex forms
34
What are inhibitors?
Molecules that interfere w/ substrate binding to active site (slowing down or stopping)
Can be reversible (competitive and non-competitive) or non-reversible
35
What is Activation Energy?
- When substrates react they need to form a complex called the transition state
- This state has higher energy levels than substrates and products
- The high temperatures are hazardous in the body (and kills cells)
- Enzymes provide a different transition state and lower activation energy
- ↓by putting stress on bonds within molecule or by holding molecules closer together
- ↑likelihood of a reaction so lowers the energy required to begin the reaction
36
How does pH affect the rate of an enzyme controlled reaction?
- Enzymes have an optimum pH (8)
- pH changes so chemical nature of amino acids can change, by adding/ removing a proton and changing the amino acids charge
- Change can result in a change in hydrogen bonds
- Meaning active site is disrupted and enzyme is denatured
37
How does temperature affect the rate of an enzyme controlled reaction?
- Work best at an optimum temperature (37.5)
- ↑means↑rate of activity as more kinetic energy to the molecules
- Meaning no. of collisions b/w enzyme and substrate will ↑so rate will too
- A much ↑ temperature causes amino acids to vibrate
- This breaks the weak hydrogen bonds and change the structure of the enzyme meaning its denatured
38
How does substrate conc. affect the rate of an enzyme controlled reaction?
- ↑substrate conc. will↑rate until enzyme is working as fast as possible
- ‘Fast as’ is when all active sites are filled all the time
- Only way to ↑rate further is ↑enzyme conc.
39
How does enzyme conc. affect the rate of an enzyme controlled reaction?
- Low conc. = great competition for active sites = low rate of reaction
- ↑conc. means more active sites =↑rate of reaction
- ↑ conc. too high has no effect as substrate conc. becomes the limiting factor
40
What is DNA?
- DNA is a polymer of nucleotides
- A nucleotide contains a Nitrogenous base, phosphate group and a deoxyribose sugar
- 4 bases: Adenine, Thymine, Guanine and Cytosine
- Form specific base pairings due to weak hydrogen bonds that form b/w them
- In a gene 3 bases in a row is called a triplet code, which codes for one amino acid
- The nucleus also contains free nucleotides
- Phosphodiester bonds form b/w nucleotides in DNA through a condensation reaction
- Which are stronger than hydrogen bonds
41
What is the structure of DNA?
- Phosphate group - obtained by eating other cells in our diet, eg. Phospholipid membranes
- Nitrogenous base - converted from amino acids from eating plant and animal proteins in our diet
- C=G triple hydrogen bond
- A=T double hydrogen bond
- In RNA A=U double hydrogen bond
42
What is DNA replication and how does it work?
- Each strand is complementary of each other
1. DNA uncoils (in a very organised way a bit at a time) and unzips (breaking hydrogen bonds)
Enzyme = DNA helicase
2. Free DNA nucleotides will join with the existing DNA molecule
Enzyme = DNA polymerase
3. Forms phosphodiester bonds b/w adjacent nucleotides
Enzyme = DNA ligase
43
What is a gene?
- A gene = a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain
- The location where a gene is found on a chromosome = locus
44
How does transcription work?
- Nucleus is Transcription
1. DNA Helicase unwinds and unzips a section of the DNA
2. Free RNA nucleotides complementary base pair with the DNA template strand, and RNA polymerase catalyses the reaction of hydrogen bonds forming b/w bases
3. RNA ligase forms phosphodiester bonds between the RNA nucleotides to produce a molecule of mRNA
45
How does translation work?
- Cytoplasm is Translation
1. The mRNA molecule diffuses out of the nucleus via a nuclear pore
2. The mRNA attaches to a ribosome, which then reads the mRNA a codon at a time
3. This triggers tRNA to bring over an amino acid that has a complementary codon
4. The tRNA molecule ‘drops off’ the amino acid, which then binds to the complementary bases, and the chain forms a protein
46
Meselson and Stahl Experiment
* Meselson and Stahl’s experiment - 15N 14N
- Grew bacteria in a growth medium containing ammonium ions as the source of N
- The type of DNA made depends on the type of Nitrogen present
- 14N is the light form of Nitrogen, while 15N is the heavier form
- Bacteria containing DNA made from 15N was allowed to divide in a solution of 14N
- The DNA was then extracted and centrifuged, and had a medium density
- This supports the semi-conservative theory b/c “the two new strands both contain one of the original parent strands”
47
Compare and contrast DNA and RNA
- Both have a phosphate group, pentose sugar and nitrogenous bases in the nucleotides
- DNA contains deoxyribose sugar while RNA contains ribose
- DNA is double stranded, while RNA is single stranded
- DNA contains thymine, whereas, RNA contains uracil
48
Compare and contrast mRNA and tRNA
- Both contain RNA nucleotides
- Both are single stranded
- mRNA doesn’t have H bonds b/w bases, but tRNA does
- mRNA is linear, whereas, tRNA is non-linear
- mRNA has a codon while tRNA has an anticodon
49
What is protein synthesis and how does it work?
- Antisense strand = template strand
- The mRNA is complementary to this
- Sense strand = what the mRNA is actually making
- If DNA is replicated from the 5’ to 3’
- Then transcription enzymes move from 3’ to 5’
- mRNA needs to be read in the correct direction by a ribosome
50
What is a mutation?
- Mutation = a change to a DNA base sequence
- A codon codes for a specific amino acid
- If a mutation occurs the wrong amino acid could be put into the polypeptide chain
- In dong so different bonds would form b/w the different R groups
- Leading to ineffective/ lack of enzyme as there would be a different tertiary structure
- Though not always as different codons can code for the same amino acid
51
What is the definition of a gene?
- Gene = a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain // a segment of a DNA molecule made up of alleles
52
What is the definition of alleles?
- Alleles = the different forms that comprise a gene
53
What is the definition of genotypes?
- Genotype = the alleles that cause the expression of the phenotype
54
What is the definition of phenotypes?
- Phenotype = how the gene is expressed in a person
55
What is the definition of Reccesive?
- Recessive = need to have a homozygous genotype to be expressed
56
What is the definition of Dominant?
- Dominant = can be a homozygous or heterozygous for the allele to be expressed
57
What is the definition of Incomplete dominance?
- Incomplete Dominance = a heterozygous condition where both alleles at a locus are partially expressed (which produces an intermediate phenotype)
58
What is the definition of Codominance?
Codominance = both alleles will be expressed as both are dominant
59
What is the definition of Sex-linked?
- Sex-linked = a disease passed through the X chromosome
60
What is the definition of a Homozygote?
- Homozygote = an individual who has two copies of the same allele at a locus
61
What is the definition of a Heterozygote?
- Heterozygote = an individual who has two different alleles at a genetic locus
62
What is prenatal screening (Amniocentesis)?
- Amniocentesis = inserting a needle through the abdomen and removing some fluid from the amniotic sac (22 weeks gestation)
63
What are the advantages of prenatal screening (Amniocentesis)?
- Confirms if abnormality is present in a fetus
- Offers a specific diagnosis chromosomal or genetic abnormality before birth
- Allows early preparation for child w/ birth defect or allows decision on abortion
- Is more accurate as baby is more developed
64
What are the disadvantages of prenatal screening (Amniocentesis)?
- Miscarriage can occur (0.5-1%)
- Mother may experience side effects
- Limited time to make the decision on carrying to full term or not
- Longer wait for results (1-2 weeks=↑stress)
65
What is Chorionic Villus Sampling?
- Chorionic Villus Sampling = inserting a needle through the vagina and removing a few cells from the early placenta (chorion) (12 weeks gestation)
66
What are the advantages of Chorionic Villus Sampling?
- Can be performed earlier than amniocentesis, meaning more time to prepare/ make a decision
- Carries less risk from an abortion if that is the decision made
- Is better at diagnosing certain conditions
- Tissue obtained is preferable for DNA analysis
67
What are the disadvantages of Chorionic Villus Sampling?
- More difficult technically than amniocentesis
- Complications, such as, miscarriage and limb deformities may occur
- Higher risk of miscarriage (2-3%)
- Is less accurate as foetus isn’t fully developed
68
What are the other types of screening?
- Preimplantation screening = screening embryos fertilised by IVF before implanted into a uterus
- Pre Symbiotic screening = screening to predict adult onset diseases
- Pre-symptomatic screening = screening to estimate the risk of developing cancer or - Alzheimer's as an adult
- Forensic/ Identity testing = screening to eg. determine the father
69
What are the Ethical/ Social/ Moral Issues with Genetic screening?
- Employers and insurers may want know and use the information gained
- The chance it is incorrect may lead to abortion of a healthy child
- Or the birth of a child with a serious disease
- May lead to medical enhancement/ design a baby
- What about people who may not be eligible/ afford the tests
- Should testing of a disease be performed on a baby if there is no cure
- The general issues with abortion // gods plan etc.
- People may not be mentally ready to know the diseases they may develop
- Will cause long term stress, especially if it’s an adult onset disease
A Level Biology (SNAB)
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