Topic 2 Flashcards
Features of Lungs - Gas exchange
Alveoli - Large SA:Vol ratio
Many capillaries - Steep concentration gradient
Constant ventilation - Steep concentration gradient
One-cell-thick walls - Low diffusion barriers
Properties of gas exchange surfaces
High surface area - High SA, Higher diffusion rate (NOT “faster” - More efficient)
Steep Conc. Gradient - Greater Conc. gradient, Faster diffusion
Gas exchange surface - Thicker gas exchange surface, Slower diffusion
Fick’s Law
Rate of diffusion is proportional to (Surface area x Difference in concentration) divided by Thickness of gas exchange surface
Cell Membrane Structure
Phospholipid bilayer - Hydrophilic phosphate head: pointing outwards - Hydrophobic lipid tails: pointing inwards
Fluid mosaic model - Contains proteins/cholesterol/glycoproteins/glycolipids - Channel proteins/Carrier proteins
Fluidity of Cell Membrane
More unsaturated lipid tails, More fluidity of membrane - Kinked lipid tails - Close packing prevented - More cholesterol, Less fluid
Evidence for fluid mosaic model
Phosphate heads darker than lipid tails - peripheral proteins easily dissociated - integral proteins not easily dissociated - Freeze-fracture studies - mouse/human membrane proteins intermixed
Osmosis
“NET” - “PASSIVE” - movement of WATER - partially permeable membrane - DOWN water potential gradient - until solution is “isotonic”
Diffusion:
“NET” - “PASSIVE” - No ATP - movement of molecules/ions - DOWN the conc. gradient - from high to low concentration
Facilitated Diffusion:
Net, “PASSIVE” movement of molecules/ions - through a membrane protein (Carrier/Channel protein) - DOWN the conc. Gradient - from high to low concentration
Active transport
Movement of molecules/ions - AGAINST the concentration gradient - Low to High conc. - Carrier protein needed - ATP hydrolysed for energy - to change shape of protein
Exocytosis
Bulk transport of substances - Out of cell - Secretory vesicle - Fuses with membrane
Endocytosis
Bulk transport of substances - Into cell - Vesicle formed from cell membrane
Channel Proteins:
Specific shape - Can be open/closed depending on presence/absence of a signal - signal can be hormonal - signal can be a change in voltage: “GATED channel”
Carrier Proteins:
Ion/Molecule binds to specific site on the protein - protein shape changes - ion/molecule crosses membrane
DNA Nucleotide
Description
Phosphate group - Deoxyribose sugar (5C)- Organic base (Adenine/Thymine/Cytosine/Guanine) - Linked by condensation reaction - Nucleotides join together by phosphodiester bonds
RNA Nucleotide
Ribose sugar (5C) - Phosphate group - Organic base (Adenine/URACIL/Cytosine/Guanine) - Linked by condensation reaction - Nucleotides join by phosphodiester bonds
DNA
Deoxyribonucleic acid - Double Helix - Sugar-phosphate backbone - Bases held together by H-Bonds - Double stranded - Polynucleotide strands are antiparallel
RNA
Ribonucleic acid - Single stranded - Can fold back on itself
Adenine - Thymine Bond
2 Hydrogen
Cytosine - Guanine Bond
3 Hydrogen
Transcription
Inside nucleus - Helicase - DNA unzips - RNA nucleotides line up against antisense strand - complementary base pairing - phosphodiester bonds form - condensation reaction - RNA polymerase - mRNA detaches from DNA
Translation
mRNA attaches to ribosome - tRNA carries specific amino acid - anticodon-codon binding; complementary - condensation reaction between amino acids - peptide bonds form - tRNA released
Triplet code - non-overlapping - degenerate
Triplet-code: Each adjacent group of 3 bases codes for one amino acid
Non-Overlapping: Each triplet is discrete and adjacent
Degenerate: Several triplets can code for the same amino acid
Gene Definition
Sequence of bases - on DNA - codes for a sequence of amino acids - on a polypeptide
Structure of Amino Acid
Central carbon bonded to…
- carboxylic acid group - Amine group - R-group (Varies) - Hydrogen
Formation of polypeptide chain
Amino acids - joined by condensation reactions - peptide bonds - into polypeptide chain (primary structure)
How 3D shape of polypeptide controls solubility
Primary structure dictates final 3D shape - Polypeptide can fold into a-helix or b-pleated sheet - interactions between R-groups influence folding - H-bonds/Disuphide bridges/Ionic interactions - Hold polypeptide chain in 3D shape
Polar R-groups on outside - Soluble
Non-Polar R-groups on outside - Insoluble
Globular proteins
Structure: tertiary/quartenary structure - hydrophilic R-groups facing outwards - spherical
Properties: Soluble, enzymes/hormones etc.
Structure + Function:
Enzymes are globular - 3D shape allows formation of enzyme/substrate complexes
3D shape - allows protein binding - e.g. Haemoglobin/Myoglobin
Fibrous proteins
Structure: little/no tertiary structure - hydrophobic R-groups facing outwards - large - repeated amino acid sequences
Properties: Insoluble, structural
Structure + Function:
Long chains - can cross-link for strength - structural molecules e.g. keratin/collagen
Insoluble - structural molecules - not broken down/absorbed etc.
Catabolic reactions
“Breaking down” - Substrate molecule broken down into smaller product molecules
Anabolic reactions
“Building up” - Substrate molecules form a larger product molecule
Lock and Key Theory
Enzyme has SPECIFIC active site - fits complementary substrate molecule(s) - Enzyme-substrate complex - bonds broken/formed - product(s) released
Induced Fit Theory
Flexible active site - substrate enters A.site - Enzyme changes shape slightly to better fit substrate - Enzyme-substrate complex - Bonds broken/formed - Product(s) released
DNA Replication
Semi-conservative - DNA unzips - Helicase catalyses - mononucleotides line up against both strands - comp. base pairing - phosphodiester bonds - condensation reactions - DNA polymerase catalyses - H-bonds form between bases
Evidence for semi-conservative replication
Bacteria grown in culture media - containing heavy nitrogen (15N) or light nitrogen (14N) - DNA extracted/centrifuged - Gen 1 had a band of DNA halfway between 15N and 14N - One DNA strand contains 15N and one strand contains 14N
In CONSERVATIVE model: - Further generations have a band at 15N
In SEMI-CONSERVATIVE model: - Further generations have bands between 14N and 15N
Types of Mutation
Frame-shift
Deletion
Substitution
Insertion
Point Mutations
Silent: Doesn’t change protein sequence - degenerate nature - same amino acid coded for by multiple codons
Nonsense: Results in coding for a stop codon - rather than amino acid - shortened protein - function impeded/non-functional
Missense: Results in a different amino acid - some missense mutations have no effect
Cause of CF
CF is caused by mutations in CFTR gene - can lead to CFTR proteins that are absent/have reduced or no function - 100s of mutation identified in CF
Effects of the CFTR mutations
In some cases ATP can’t bind to & open ion channels - or channel is open but chloride ion transport is reduced
Less chloride transport into mucus - less sodium ion movement into mucus down E.C gradient - less water movement into mucus - sticky mucus
Gene definition
Sequence of bases - on DNA - codes for amino acid sequence in polypeptide
Allele definition
Alternative form of a gene - found at the same locus - on DNA
Effect of CF on Gas Exchange
Chloride ions not moved into mucus - Water does not move out of cells - sticky mucus - Not cleared by cilia/coughing
Sticky mucus decreases gas exchange - decreases surface area of lungs by blocking alveoli - less diffusion of gases - diffusion barrier is thicker - slower diffusion of gases
Frequent lung infections - dirt and pathogens get trapped and cannot be cleared
Effect of CF on Digestion
Chloride ions not moved into mucus - Water does not move out of cells - sticky mucus
Sticky mucus blocks pancreatic duct - digestive enzyme release impaired - lower rate of digestion - enzymes trapped damage pancreas - cause cysts of hard, fibrosed tissue (hence cystic fibrosis) - could cause a form of diabetes
CF patients have higher daily energy requirement - might need to take digestive enzyme supplements
Effect of CF on Reproduction
Males: Vas deferens blocked/absent - fewer/no sperm reach egg - reduced fertility
Females: mucus plug develops in the cervix - reduced fertility
Ways to test for CF in embryo
Chorionic villus sampling
Amniocentesis
Non-invasive prenatal diagnosis
Pre-implantation genetic testing
Amniocentesis process
Invasive - Needle inserted into amniotic fluid - fetal cells collected - between 15-17 weeks - 1% miscarriage risk
Chorionic villus sampling process
Invasive - small sample of placental tissue removed - through abdomen wall/vagina - between 8-12 weeks - 2% miscarriage risk
Non-invasive prenatal diagnosis
“Cell free fetal DNA” fragments in mothers blood analyzed - 7-9 weeks - different tests require different concentrations of cffDNA
Pre-implantation genetic testing process (Only IVF)
Family history of serious genetic condition - IVF embryo - when embryo has 8 cells, one is removed and tested - DNA analysed
Pros and Cons of IVF:
IVF avoids need for possible abortion
Expensive, stressful and low success rate
Issues with testing for CF
Might go against beliefs of family - false positive might lead to abortion of healthy fetus - false negative might lead to a family not being ready to raise a genetically abnormal kid - carries a miscarriage risk
CORE PRACTICAL 3:
Investigate membrane structure, including the effect of alcohol concentration or temperature on membrane permeability.
plant of 5 different “variants” (e.g. age) - same mass/surface area - Heat plant samples to different temp/add different concentrations of ethanol - colorimeter to measure permeability
CPAC 4 Investigate the effect of enzyme and substrate concentrations on the initial rates of reactions.
at least 5 concentrations of substrate/enzyme - same volume - Method of measuring dependent variable (e.g. time for color change - if indicator is used, ABSORBANCE)
