1
Q
Features that increase the rate of gas exchange
A
- Lots of alveoli = large surface area for diffusion to occur across
- alveolar epithelium and capillary endothelium are each only one cell thick = short diffusion pathway
- all alveoli have good blood supply from capillaries —> they constantly take away oxygen and bring carbon dioxide maintaining the concentration gradient
- breathing in and out refreshes the air in the alveoli keeping the concentration gradient
2
Q
Properties of gas exchange surfaces
A
- the surfaces have a high volume to surface area ration e.g. alveoli
- they surfaces are thin so there is a short diffusion pathway
- the organism also maintains a steep concentration gradient of gases across the exchange surface
3
Q
Ficks Law
A
Rate of diffusion = (area of diffusion surface x difference in concentration) / thickness of diffusion surface
Fick’s law calculates rate of diffusion
4
Q
Phospholipid molecules in the membrane
A
- head contains phosphate group it is hydrophilic (attracts water)
- tail is made of two fatty acids it is hydrophobic (repels water)
- because of this the molecules automatically around themselves into a bilayer
- with the tails face inwards making the inside hydrophobic
- and the heads facing outward on either side of the membrane
- this means the membrane doesn’t allow water soluble substances like ions through it
5
Q
Fluid Mosaic other molecules in the phospholipid bilayer
A
-protein molecules are scattered through the bilayer
(Like tiles in a mosaic)
- because the phospholipid bilayer is fluid, the proteins can move around within in it
- proteins that have a polysaccharide attached are called glycoproteins
- some lipids also have a polysaccharide chain attached to them these are called glycolipids
- cholesterol is also present in the membrane it’s fits in between the lipids forming bonds with them —> this makes the membrane more fluid
- channel proteins allow larger molecules and ions to pass through the membrane
6
Q
Osmosis
A
Osmosis is the diffusion of free water molecules across a partially permeable membrane from an area of higher concentration of water molecules to an area of lower concentration of water molecules
7
Q
Facilitated diffusion: carrier and channel proteins
A
Carrier proteins:
- move large molecules into and out of the cell down their concentration gradient
- different carrier proteins facilitate the diffusion of different different molecules
1/ a larger molecule attaches to a carrier protein
2/ the protein changes shape
3/ realises the molecule on the other side of the the membrane
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
8
Q
Active Transport
A
- a molecule attaches itself to the carrier protein
- the protein changes shape
- the molecule is released on the other side
- difference between Active transport and facilitated diffusion using carrier proteins: energy is used in Active transport
—> this energy comes from ATP - ATP is produced by respiration
- it’s an immediate source of energy
- when ATP is hydrolysed the energy is released
- this allows the molecule to move against its concentration gradient
9
Q
Endocytosis
A
- some molecules are too large for carrier proteins
- instead the cell surrounds a substance with a section of its cell membrane
- the membrane forms a vesicle inside the cell containing the ingested substance
- also uses ATP for energy
10
Q
Exocytosis
A
- substances produced by the cell need to be released by the cell e.g. digestive enzymes and lipids need to be released from the cell
- vesicles containing these pinch off from the sacs in the Golgi apparatus and move towards the cell membrane
- the vesicles fuse with the cell membrane and release their contents outside of the cell
- membrane proteins are inserted straight into the cell membrane
- exocytosis uses ATP as an energy source
11
Q
Globular Proteins
A
- round compact proteins made up of multiple polypeptide chains
- chains are coiled up so that the hydrophilic parts are on the outside and the hydrophobic parts are on the inside
- this makes them soluble —> easily transported in fluids
- e.g. Haemoglobin
12
Q
Fibrous Proteins
A
- long, insoluble polypeptide chains —> tightly coiled around each other to form a rope shape
- the chains are held together by lots of bonds e.g. disulphide and hydrogen bonds which make the proteins strong
- because they are strong they are found in supportive tissue
- e.g. collagen
13
Q
Primary Structure (inc. bonds)
A
- The sequence of amino acids in the polypeptide chain
- amino acids are linked together by condensation reactions
- peptide bonds hold together the amino acids and therefore the primary structure
- the amino aid sequence determines what bind will from and how the protein will fold up into its 3D structure
- determines 3D structure and properties
14
Q
Secondary Structure (inc. bonds)
A
- polypeptide chain does not remain straight and flat
- hydrogen bonds form between the amino acids in the chain
- making it automatically coil up into an alpha helix or a beta pleated sheet
15
Q
Tertiary Structure (inc. bonds)
A
- the coiled or folded chain of amino acids is often folded further
- more bonds form between the different parts of the polypeptide chain:
- ionic bonds: attractions between negative and positive charges on different parts of the molecule
- Disulfide bonds: whenever two molecules of the amino acid cysteine come into close contact the sulphur Atom in one cysteine bonds to the the sulphur in the other (forming a disulfide bond)
- Hydrophobic and Hydrophilic interactions:
Hydrophobic groups automatically clump together this makes the hydrophilic groups get pushed to the outside this affects how the protein folds up into its final structure - hydrogen bonds
- the tertiary structure forms the final structure of proteins made from a single polypeptide chain
16
Q
Structure of amino acids
A
R group
Amine or amino group -NH2
Carboxyl group -COOH2
17
Q
Fluid mosaic model is partially permeable this means…
A
… small molecules can move through the gaps in between the phospholipids but larger molecules but use methods of facilitated diffusion
18
Q
What do enzymes do
A
- catalyse metabolic reactions
e. g. cellular = respiration and organism = digestion
19
Q
intracellular and extracellular
A
- intracellular = enzyme catalyses reactions inside the cell
- extracellular = enzyme catalyses reactions outside of the cell
20
Q
what is an enzyme
A
- protein
- that catalyse chemical reactions by working as biological catalysts
21
Q
structure of enzymes
A
- active site: specific shape, where the substrate binds
- highly specific due to their 3D structure, only catalyse specific reactions
22
Q
How do enzymes speed up reactions?
A
- enzymes lower the energy required for a reaction to start (activation energy) of reactions
- this speeds up the rate of reaction
- they reduce the repulsion between molecules that need to be bonded - bond more easily
- active site puts a strain on molecules that need to be broken down - break down more easily
23
Q
Lock and Key Model
A
- enzyme is the lock
- substrate is the key
- active site of enzyme is specific to a particular substrate the same way a lock has a specific key
24
Q
Induced Fit Model
A
- explains why enzymes are so specific and only bind to certain substrates
- must be the right shape AND be able to make the active site change shape the right way
25
Tertiary structure of enzyme
- specific, usually only catalyse one reaction
- this is because only one complementary substrate will fit the active site
- active site shape is determined by tertiary structure which is determined by the primary structure of an enzyme
- tertiary structure altered = substrate doesn't match active site = not enzyme-substrate complete and no catalyzed reaction
- tertiary structure may be altered by pH or temperature or mutation in primary structure
26
enzyme concentration affects the rate of reaction
- the more enzyme, the more active sites and the more likely a collision between the substrate and enzyme is
- therefore more likely to form enzyme-substrate complex and the rate of reaction is increased
- but if amount of substrate is limited there may become a point where there is more enzyme than substrate
- in this case adding enzymes has no further effect on the rate of reaction
27
substrate concentration affects the rate of reaction --> up to a point
- more substrates = more collisions = more enzyme-substrate complexes = faster rate of reaction
- even MORE substrates = over saturation = all active sites full = rate of reaction will not become any faster
28
initial rate of reaction - why at start?
- substrate concentration inevitably decreases with time during the reaction
- so therefore rate of reaction will also decrease over time
- initial rate of reaction = highest rate of reaction (fastest)
29
Similarities between DNA and RNA
- BOTH RNA and DNA contain a pentose sugar
- BOTH RNA and DNA contain a phosphate group
- BOTH RNA and DNA are polymers of nuclotides
30
Differences between DNA and RNA
- DNA is double-stranded WHEREAS RNA is single-stranded
- DNA has a deoxyribose pentose sugar WHEREAS RNA has a ribose pentose sugar
DNA uses the base thymine WHEREAS RNA uses the base uracil
31
DNA
- phosphate, deoxyribose pentose sugar and base
- double-stranded
- bases: adenine, cytosine, guanine and thymine
- Double helix
- Strands are anti-parallel
- A-T with two hydrogen bonds
- C-G with three hydrogen bonds
32
RNA
- phosphate, ribose pentose sugar and base
- single stranded
- uracil, cytosine, guanine and adenine
- U-A and C-G
33
mRNA
- made in the nucleus during transcription
- three adjacent bases = codon
- carries genetic code from the DNA in the nucleus to the cytoplasm
34
tRNA
- found in the cytoplasm
- amino acid binding site at one end
- sequence of 3 bases (anticodon) at the other end
- brings amino acids that are used to make proteins to the ribosomes during translation
35
The Genetic Code is....
Non-overlapping : base triplets or codons do not share bases, each triplet is separate from the one before and the one after it
Degenerate: more than one triplet code for the same amino acid
36
Transcription words to include (add an explanation on own - prompts)
- nucleus
- DNA Helicase
- unzip
- hydrogen bonds
- unwinds
- exposes bases
- sense strand and antisense strand
- free RNA mononucleotides
- complementary base pairs to template strand
- T-->U
- RNA Polymerase
- joins bases
- DNA Helicase unwinds more
- moves along until 'stop codon'
- detaches
- moves out
- nuclear pore
37
Translation words to include (add an explanation on own - prompts)
- mRNA attaches
- Ribosome
- tRNA brings amino acids
- complementary bases to start codon
- attaches
- second complementary attaches
- amino acids
- join
- peptide bonds
- tRNA moves away
- ribosome moves along
- more tRNA molecules
- complementary bases
- more amino acids
- tRNA moves away
- continues until stop codon
- amino acid polypeptide chain
- (primary structure)
38
Semi Conservative Replication
- DNA helicase breaks hydrogen bonds
- helix unwinds to form two single strands
- each original strand acts as a template strand
- complementary base pairs are attracted to the exposed bases
- ATCG
- condensation reactions join the new strands together
- catalysed by DNA polymerase
- hydrogen bonds form between the bases
- each new DNA molecule has one original DNA strand and one new strand
39
Meselson and Stahl's evidence for semi-conservative DNA replication
- conservative = two new strands for whole new DNA molecule rather than half and half
- 2 samples of bacteria were grown in nitrogen broth
- 1 in heavy nitrogen and 1 in light nitrogen
- as the bacteria reproduced, nitrogen was taken up from the broth to make DNA nucleotides
- nitrogen became part of the DNA
- sample from each batch = centrifuge
- heavy nitrogen DNA settled lower than light nitrogen DNA because it is heavier
- the heavy nitrogen DNA was put in light nitrogen birth and left for one round of DNA replication
- placed back in centriguge
- DNA settled in the middle - showing that each DNA molecule was half heavy and half light --> proving semi conservative theory
if the conservative theory had bee correct:
The original DNA strand (heavy) would have settled at the bottom and the new DNA strand (Light) would have settled at the top
40
Types of DNA mutation/errors that can occur during replication
Substitution: one base is substituted with another
Deletion: one base is deleted
Insertion: one extra base is added
Duplication: one or more bases are repeated
Inversion: a sequence of bases is reversed
41
consequences of mutations during DNA replications with reference to cystic fibrosis
- the primary structure could be altered
- change in base sequence could change which amino acids are coded for
- this could change the final 3D shape of a protein - so it doesn't work properly
- a mutation in a gene can cause genetic disorders
- e.g. cystic fibrosis is caused by a mutation in a gene
- over 1000 possible mutations are responsible for cystic fibrosis
42
Gene
- a sequence of bases that code for a protein
43
Allele
- a different version of a gene e.g. allele for green eyes or allele for blue eyes are both genes for eye colour
44
Genotype
- The alleles a person has
45
phenotype
the physical characteristics displayed by an organism e.g. blue eyes
46
Dominant
An allele whose characteristic appears in the phenotype even if there's only one copy present e.g. if the allele for blue eyes is dominant (B) it is express if Bb or BB
47
Recessive
An allele whose characteristic only appears in the phenotype if there are 2 copies present e.g. bb
48
Incomplete dominance
the trait from the dominant allele isn't shown completely over the trait from the recessive allele
e.g. flowers: snapdragons have alleles for red flowers: RR, white flowers: rr and pink flowers: Rr
49
Homozygote
an organism has 2 copies of the same allele for a certain characteristic: BB or bb
50
Heterozygote
an organism has two different alleles for a certain characteristic: Bb
51
Carrier
- if a recessive allele can cause a disease, a carrier has one dominant and one recessive allele
- they won't have the disease but they carry one copy of the allele for the disease
52
Cystic fibrosis is caused by:
- a mutation in the gene that codes for CFTR protein
| - CFTR is a channel protein
53
The cystic fibrosis mutation causes:
- CTFR is a channel protein
- transports chloride ions out of cells and into the mucus
- this causes water to move into the mucus through osmosis
- which makes the mucus watery
- Mutant CFTR is less efficient at moving chloride ions into the mucus
- so people with CF ha abnormally thick and sticky mucus
- this causes problems in the respiratory, digestive and reproductive systems
54
CF and the respiratory system
- mucus is supposed to help prevent lung infections by trapping microorganisms
- this mucus is then moved towards the throat by cilia
- in people with CF:
- the thick and sticky mucus makes the cilia unable to move
- making mucus build up in the airways
- some airways become completely blocked by mucus
- surface area
55
CF and the digestive system
- the tube that connects the pancreas to the small intestine can become blocked with mucus
- preventing digestive enzymes from reaching the small intestine
- reducing ability to digest food and so fewer nutrients are absorbed
- mucus lining of the small intestine is abnormally thick --> preventing nutrient absorption
56
CF and the reproductive system
- the tubes connecting the testicles to the penis are absent or can be blocked with mucus --> so sperm cannot reach the penis
- thickened cervical mucus can prevent the sperm from reaching the egg - thick mucus reduces the motility of the sperm, reducing its chances of reaching the egg
57
three main uses of genetic screening
1. identification of carriers
2. preimplantation genetic diagnosis
3. prenatal testing
58
identification of carriers: explained
- offered to people with a family history of genetic disorders
- shows whether people without a disorder carry an allele that can cause a disorder
- allows couples to determine the likelihood that their children will have a disorder
- allows people to make informed decisions on whether to have children and/or whether to have prenatal testing
59
identification of carriers: social and ethical issues
- may cause emotional stress
- could affect your ability to find a partner
- tests arent always 100% accurate - could give a false result
60
Preimplantation genetic diagnosis (PGD): explained
- carried out on embryos produced by IVF
- screens embryos before implantation
- reduces chances of having a baby with a genetic disorder --> only embryos without genetic disorders will be implanted
61
Preimplantation genetic diagnosis (PGD): social and ethical issues
- can be used to find out other characteristics e.g. gender and eye colour --> may lead to embryos being selected for other characteristics in the future (designer babies)
- False results = incorrect information
62
Prenatal testing
- screening unborn babies for genetic disorders
- offered to pregnant women with a family history of genetic disease
- amniocentesis or chronic villus sampling
- allows parents to make informed decisions: choose abortion, or prepare for future care for the child
- any medical treatment needed could be started at birth
63
amniocentesis
- 15-20 weeks
- sample of amniotic fluid taken with a needle
- fluid contains fetal cells that contain DNA which can be analysed
- 1% miscarriage risk
- results = 2-3 weeks
- rapid test (common disorders) 3-4 days
64
Chronic Villus Sampling - CVS
- 11-14 weeks
- earlier decision can be made
- sample of cells taken from chronic villi - part of the fetus that connects to the mother
- the cells contain DNA that can be analysed
- 1-2% risk of miscarriage
- results = few days + more details in 2+weeks
65
Prenatal testing: social and ethical issues
- increase risk of miscarriage
- false results
- some people may consider it unethical to abort a fetus because it has a genetic disorder
SNAB Biology
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