Topic 2 Flashcards
Diffusion
Net movement of particles Down a the concentration gradient (high ->low) Across a partially permeable membrane Particles diffuse both ways Passive process
Gas Exchange Surfaces
Large surface area to volume ration
Thin -> short diffusion pathway
Steep concentration gradient maintained
Features of Lungs
- Lots of alveoli -> large SA
- Alveolar epithelium and capillary endothelium = 1 cell thick -> short diffusion pathway
- Good blood supply (maintain conc. gradient)
- Breathing -> refreshes air + mantain conc. gradient
Lungs gas exchange surface
Alveolar epithelium
Alveoli process
- oxygen diffuse out of alveoli
- Crosses the alveolar epithelium (thin, flat cell layer) + capillary endothelium -> blood
- Carbon dioxide diffuses into the alveoli -> breathed out
Lung structure
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Alveoli structure
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Fick’s Law
rate of diffusion ∝ (area of diffusion surface x difference in concentration / thickness of diffusion surface)
P x A x ((C1 - C2) /T)
= Rate ; Fick's Law P = permeability constant A = surface area (C1 - C2) = difference in concentration T = thickness in exchange surface
Cell membranes
‘Fluid Mosaic’ Structure (suggested in 1972)
Phospholid bilayer -> fluid = lipids constantly moving
Partially permeable:
- gaps inbetween phospholipids -> small molecules pass through
- membrane proteins (Channel + Carrier) -> large molecules + ions
Phospholipid bilayer
Phospholipid:
- Head = phosphate group -> hydrophillic
- Tail = two fatty acids -> hydrophobic
Bilayer:
- Two phospholipids
- Automatic bilayer of heads facing water outside/inside membrane
- Centre = hydrophonic -> water solubles cannot enter
Fluid Mosaic Model
- Fluid = Phospholipid bilayer (fluid lipids can switch adjacently and opposite but rare, tend to move linearly)
- Mosaic = protein molecules scattered throughout ( can move around)
- Glycoprotein = protein + polysaccharide chain
- Glycolipid = lipid + polysaccharide chain
- Cholestrol between phospholipids -> forms bonds -> membrane = more rigid
- Channel + Carrier Proteins
Osmosis
H2O diffuses across partially permeable membrane
Down concentration gradient
Diffuses both ways -> net movement to lower side
Active Transport
Moves molecules + ions against the concentration gradient
Across a plasma membrane
Requires energy from ATP
Active Transport mechanism
- Molecule attaches to carrier protein -> changes shape
- Molecule moved across plasma membrane -> released
- Energy used = ATP:
- produced via respiration (immediate energy source)
- ATP hydrolysed -> energy released
Facilitated Diffusion
Passive transport via carrier + channel protein diffusion
Larger molecules:
- amino acids
- glucose
Different carrier proteins facilitate different molecules
Facilitated Diffusion mechanism
- Large molecule attaches to carrier protein
- Protein changes shape
- Releases molecule on opposite side of membrane
Channel proteins
Different for each +ve/-ve particle
Form pores in membrane for charged particle diffusion
Endocytosis
Large molecules:
- protein
- lipids
- (some) carbs
1. cell surrounds substance with membrane section
2. membrane pinches off -> vesicle formed in cell (contains ingested substance)
3. requires ATP
Phagocytes
White blood cell
Perform endocytosis for dead cells + microorganism
Exocytosis
Secreted substances produced by the cell:
- digestive enzymes
- hormones
- lipids
1. Vesicles pinch off from golgi apparatus sacs -> cell membrane
2. Vesicle fuses with membrane -> secretes substance outside the cell
3. Some substances inserted straight into the membrane
4. requires ATP
Proteins
Monomers = amino acids Dipeptide = 2 amino acids Polypeptide = 2+ amino acids Protein = 1 or more polypeptides
Amino Acids
Same general structure:
-Amino/Amine group (H2N) + Variable group (R) + Carboxyl group (COOH)
Variable group = carbon containing R group
Bank of 20 amino acids (variation of R)
e.g H2N - RCH - COOH
e.g. Alanine = H2N - (CH3)CH - COOH
Polypeptides
Formed via condensation reactions:
- H from amine/amino group
- OH from carboxyl group
Peptide bonds = bonds between amino acids
Primary Protein Structure
Sequence of amino acids in polypeptide chain
Determines bonds -> folds in 3D structure
Secondary Protein Structure
Hydrogen bonds form between amino acids in chain:
- Coils into Alpha helix
- or Folds into Beta pleated sheet
Tertiary Protein Structure
Coiled/Folded further -> 3D structure
- hydrogen + ionic bonds form between different polypeptide
- disulphide bond (if cysteine = amino group, is present)
- if a single pp chain = final 3D tertiary structure
note: bonds determine properties + structure
Quaternary Protein Structure
Several different polypeptide chains combined via bonds
e.g. haemoglobin, collagen, insulin
The different bonds of the 4 (protein) structural levels
Primary = peptide Secondary = hydrogen Tertiary = ionic - disulphide (cysteine present) - hydrophobic interactions (groups clump together_ - hydrophillic (pushed outside - hydrogen bonds Quaternary = determined by tertiary
3D structures
Globular
Fibrous
Globular protein structure
- round + compact; many polypeptide chains
- chains coiled up:
- hydrophillic face outwards
- hydrophobic face inwards - soluable -> easily transported
Haemoglobin structure
Globular protein
4 polypeptide chains:
- iron containing haem group bonds to oxygen (deoxyhaemolobin -> oxyhaemolobin)
Soluable -> transported via red blood cells
Fibrous protein structure
- long chains
- insoluable
- rope shape (chains highly coiled around one another
- lots of bonds -> strong protein -> often supportive tissue
e. g. Collagen = connective tissue
Collagen structure
3 polypeptide chain
Wound together in alpha helix
Very strong
Enzymes
Biological catalysts for metabolic reactions:
- Cellular level (respiration)
- whole organism (e.g. digestion)
- affect structure + function
- are Extra or Intra (cellular)
- are proteins
- have and active site (with specefic shape)
- substrate fits into AS - highly specefic
- related to tertiary structure - lower activation energy of a reaction:
- 2 substrates held close together -> reduces repulsion
- breakdown -> fitting into AS strains bonds -> break down easier
note: energy released as product forms
Lock + Key model
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‘Induced Fit’ model
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Enzyme properties
Due to 3D (tertiary) structure (determines shape, in turn determined by primary structure)
- Very specific - only one complements substrate -> AS -> catalyse one reaction
- Different enzyme -> different tertiary structure -> different shapes AS
- Tertiary shape altered -> alters AS -> stops E-S complex
- caused by pH and Temp - Primary structure determined by gene
- mutation -> different enzyme structure
Enzyme concentration > substrate concentration
More active sites
More likely substrate + AS collide -> form E-S complex
Increases rate of reaction
Steadily increases as more AS available (graph)
Note: substrate concentration = limiting factor
Enzyme concentration < substrate concentration
More substrate = more likely collisions
- true up to saturation point = AS full
Substrate concentration decreases over time
- no variable change = decreased reaction
- initial rate = highest
DNA
Deoxyribonucleic Acid
Stores genetic info Two polynucleotide strands Polymer of mononucleotides: - Pentose sugar (Deoxyribose) - Phosphate group - Nitrogen containing organic base
DNA nitrogen containing base variables
- Guanine
- Cytosine
- Adenine
- Thymine
RNA
Ribonucleic Acid
Transfers genetic info from DNA -> ribosomes - ribosomes read RNA - make polypeptides (via translation) Polymer of mononucleotide - Pentose sugar (Ribose) - phosphate group - base variables One polynucleotide strand
RNA base variables
- Guanine
- Cytosine
- Adenine
- Uracil
Sugar phosphate backbone
Mononucleotide joined via a condensation reaction
- between phosphate group of one and sugar group of another
- water = byproduct
DNA structure
Double helix structure
- Two polypeptide strands joined via hydrogen bonds between bases
- Complementary base pairing:
- A -T
- C - G
- equal amount of paid within molecule - Hydrogen bonds between complementary pairs:
- A - T = three
- C - G = two - Strands are anti parallel
- Twist -> anti parallel
When was the double helix determined?
1953 by Watson and Crick
Previously protein was believed to hold genetic code as more chemically varied compared to DNA’s simplicity
Gene
Sequence of mononucleotide bases on a DNA molecule that code for amino acids in a polypeptide
- different proteins = different amino acid numbers + orders
- order of mononucleotide bases in gene -> order of amino acids in protein
- triplet = sequence of three bases that code for an amino acid
- sequence of bases in DNA = template for proteins -> protein synthesis
mRNA
Messenger RNA
- made in nucleus during transcription
- CODON = three adjacent bases
- carries DNA genetic code from nucleus -> cytoplasm
tRNA
Transfer RNA
- located in the cytoplasm
- amino acid binding site + sequence of three bases (ANTICODON) at either end
- carries amino acids to ribosomes during translation
DNA copied into RNA for protein synthesis
DNA molecules found in the nucleus
Organelles for protein synthesis (ribosomes) in cytoplasm
DNA = too large to move out of nucleus
Section is copied into mRNA = transcription
mRNA leaves the nucleus
Joins with ribosome in cytoplasm -> translation process
Genetic code =
Non-overlapping:
- sequence of base triplets/codons which code for specific amino acids
- > triplet is read in sequence & do not overlap
Degenerate:
- more possible triplet combos than amino acids
- 20 amino acids
- 64 triplets
- some amino acids = 1+ triplet
- > e.g. tyrosine = ‘UAU’ or ‘UAC’
Start + stop codons = production signals
- UAG = stop codon
Transcription (protein synthesis)
- RNA polymerase attaches to DNA double helix at a gene’s start codon
- Hydrogen bonds between polypeptide strands in the gene break -> unwinds DNA
- Strand used as template for mRNA copy
- RNA polymerase lines up free RNA mononucleotide alongside template
- complementary bases paired (e.g. T -> U) -> complementary strand
- RNA mononucleotide then joined by RNA polymerase -> mRNA - RNA polymerase moves along DNA -> strands separate (mRNA assembled)
- Hydrogen bonds reform once RNA polymerase bases
- strand winds up in double helix - RNA polymerase reaches stop codon -> detaches from DNA
- mRNA moves out of nucleus via nuclear pore
- attaches to ribosome in cytoplasm
Translation (protein synthesis)
- mRNA attaches to ribosome
- tRNA carry amino acids to ribosome
- tRNA molecule (an anticodon = complementary to mRNA start codon) attaches to mRNA molecule
- Second tRNA attaches to next codon in chain via complementary base pairing
- Two amino acids on tRNA’s attached via peptide bonds
- first tRNA detaches - Ribosome moves onto next codon
- tRNA repeat process, producing chain of polypeptides until stop codon
- Polypeptide chain moves away from ribosome
Note: ribosome deals with two tRNA molecules at a time
Semi-conservative replication
DNA copied before cell division
Half of DNA strands from each new helix are from the original
-> genetic continuity between generations
Semi-conservative replication process
- DNA helicase breaks H-H bonds between bases on polynucleotide strands -> unwind
- Original strands act as templates -> complementary base pairing:
- free floating DNA nucleotides attracted to complementary exposed bases - Condensation reactions catalysed by DNA polymerase
- nucleotides join
- H-H bonds reform - Each new DNA helix has one original polynucleotide strand & one new one
Conservative Replication
Original DNA molecule stays together
Genetic Mutations
Mutations = changes to base sequence of DNA
Caused by errors in DNA replication (usually):
- substitution = one base replaced with another
- deletion = one base is deleted
- insertion = extra base added
- duplication = one+ bases repeated
- inversion = base sequence reversed
Order of DNA bases -> order of amino acids -> primary structure of protein -> 3D shape
Causes Genetic disorders (lots of different mutations possible e.g. CF caused by 1,000+)
Gene
A sequence of bases on a DNA molecule that codes for a protein which results in a certain charecteristic
Allele
A different version of a gene; usually there are two types
Genotype
The alleles a person has
Phenotype
Charecterisitics displayed by an organism
Dominant
Only one copy of an allele is needed to appear in the phenotype (R)
Recessive
Two copies of the allele required to appear in phenotype (r)
Incomplete dominance
Trait of a dominant allele is not completely shown over trait of recessive allele
Both alleles influence phenotype
E.g. snapdragons: red (RR), white (rr), pink (Rr)
Homozygote
Organism copies two copies of same allele for a characteristic
Heterozygote
Organism carries two different alleles for a characteristic
Carrier
A heterozygote who has a recessive allele which is disease causing, but does not themselves have the disease
Genetic diagrams
T t
T TT Tt
t Tt tt
= 50℅ Tt, 25℅ TT, 25℅ tt
3:1 genetic ratio for recessive phenotype
Genetic Pedigree Diagrams
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Cystic Fibrosis (CF)
- Caused by gene mutation that codes for CFTR protein
- CFTR = Cystic Fibrosis Transmembrane conductance Regulator - CFTR = channel protein
- transports chloride ions out of cell -> mucus
- causes H2O to move into mucus by osmosis -> watery - Mutation -> less efficient at transport
- mucus = thick + sticky
- causes problems in: respiratory, digestive and reproductive systems
CF + Respiratory system
- Mucus helps prevent lung infection -> traps microorganisms
- transported to throat by cilia - Cilia unable to move mucus (thick + sticky)
- Mucus builds in airways
- Some airways become completely blocked
- > gas exchange cannot occur below blockage - SA available for gas exchange reduced -> breathing difficulties
- More prone to lung infection
- antibiotics -> stop microorganisms
- physiotherapy -> dislodge mucus
CF + digestive system
- Tube connecting pancreas to small intestine becomes blocked
- > prevents digestive enzymes from reaching small intestines
- > reduced digestive ability -> less nutrients absorbed - Mucus can cause cysts to form in pancreas
- > inhibit enzyme production - Mucus lining in small intestine abnormally thick
- > inhibits nutrients absorption
CF + reproductive system
- Prevent production & transportation of gametes
- In men (usually):
- tubes connecting testicles to penis are absent or blocked -> sperm has no access - In women (usually):
- thickened cervical mucus prevents sperm reaching egg (reduced sperm motility)
Genetic screening - Identification of carriers
Informed decisions (having children + prenatal testing)
Social issues = finding a partner + emotional stress
Ethical issues =
- false results -> incorrect info etc
- employers/life insurance companies -> genetic discrimination
Genetic screening - PGD
Pre-implantation Genetic Diagnosis
- carried out on embryos produced by IVF
- screening before implantation
- avoids abortion + implantation of a genetically mutated embryo
- issues: false results, finding out other characteristics (designer babies)
Genetic Screening - Amniocentesis
- 15 - 20 weeks of pregnancy
- amniotic fluid sampled via abdomen ( v. Fine needle)
- fluid contains fetal cells -> DNA
- 1℅ risk of miscarriage
- results = 2-3 weeks (conclusive), 3-4 days (basic)
Genetic screening - Chorionic Villus Sampling (CVS)
- 11-14 weeks of pregnancy
- cells taken from chorionic villi via abdomen (needle)
- or vagina (catheter = thin, flexible tube)
- 1-2℅ risk of miscarriage
- results = two+ weeks (in depth/detailed), few days (initial/obvious)
Chorionic Villi
Villi that provide maximum contact area between the fetus and the mothers blood via the placenta
