2: Genes and health

LUNGS: Allow rapid gas exchange between atmosphere and blood.

Air drawn in via trachea goes into lungs LOW PRESSURE< created by movement of ribs and diaphram

ALVEOLI:Site of gas exchnage

Diagram of structure of lungs:

Thin coating of mucus in tubes of gas exchange system-pruduces by goblet cells.

Mucus traps dust and debris → Removed by wave motion of cilia.

Cilia cover the epithelial cells that line the tubes of the gas exchange system.

In walls of alveoli and capillaries the epithelium is squamous (or pavement)

Made of protein fibres in jelly-like MATRIX

In trachea, bronchi and bronchioles there are ciliated epithelial cells

People with CF have drier mucus resulting in sticky mucus layer<hard 4 cilia to remove.

People with CF: ∴ have increased chance of lung infection & gas change is less efficient.

• Harmful bacteria can thrive in these anaerobic conditions

O2 and CO2 diffuse acros the walls of the alveoli into the blood system.

Rapid gas exchange needed ∴ we are adapted:

• Fine structure of lungs
• Alveoli have large surface area to quicken rate
• Lots of capillaries around alveoli
• Thin walls for easier diffusion of substances in and out of cell

Surface area to vlume ratio: Total SA / volume

Rate of diffusion dependent on: SA, Conc. gradient & thickness of gas excange surface

∴Fick's Law: Rate of diffusion= Surface area x diference in concentration

. ............................................ thickness of the gas exchange surface

Amino acids (20)-->Proteins

All amino acids contain:

• NH2 (Amine grp)
• -COOH (Carboxylic grp)
• H- Attached to a central carbon atom
• Each type of amino acid has a different side chain--- the R group (residual)

General structure of an amino acid:

Primary structure: Made up of a sequence of amino acids via CONDENSATION reactions. PEPTIDE BOND

Secondary structure: α helices or β-pleated sheets due to amino acid interactions ∴ twists/ folds to 3D shape. HYDROGEN BOND

Tertiary and quaternary: Chemical bonds and HYDROPHOBIC INTERACTIONS between R GRPS maintain final structure of protein.

Conjugated: have another chemical grp associated with their polypeptide chain(s).

Globular: pp chain folded into compact spherical shape. SOLUBLE--> hydrophilic side chains

Fibrous: Long chains.Pp chains can be cross linked 4 strength. INSOLUBE.

Phospholipid bilayer: Two layers of phospholipids.

Phospholipid: Phosphate head and two fatty acids tails.

THE FLUID MOSAIC MODEL

As well as a phospholipid bilayer on the cell surface membrane, it also has proteins, cholesterol and glycoproteins and glycolipids.

Some span the membrane, are only found within the inner layer or only found within the outer layer.

Some proteins fixed (intergrated) and some are not (peripheral).

Fluid: Phospshates are not in a fixed position- can move

Mosiac: Glycolipids etc dotted around membrane in mosaic pattern

Model: Theory formed to provide explanation

Evidence for fluid mosaic model

Hydrophilic head more dense & shown in electron micrograph

Phosphates arrange themselves in a more stable position (due to non/ polarity)- bilayer

• Diffusion
• Osmosis
• Active Transport
• Exocytosis
• Endocytosis

Diffusion: The movement of particles from a region of high conc. to a region of low conc. down a concentration gradient.

Facilitated diffusion: The movement of hydrophobic moelcules or ions from a high to low conc. through channel or carrier proteins. (PASSIVE)

Osmosis: The movement of water molecules from a high to low conc. through a partially permeable membrane.

Active Transport: (requires specific carrier proteins that change shape). Against conc. gradient so requires (ATP) energy for movement from low to high conc.

Exocytosis: Used for bulk transport of substances out of cell. Vesicles fuse with the cell surface membrane,releasing contents.

Endocytosis: Used for bulk transport of substances into the cell. Vesicles are created from cell surface membrane, bringing their contents into cell.

Too much H2O: 1. Na+ actively pumped across basal membrane

2. Na+ diffuses through sodium cahnnels in apical membrane (electrcal gradient forms)

3. Cl- diffuses down electrical gradient

4.Water drawn out of cells by smosis due to high salt conc. in tissue fluid

5. Water drawn out of mucus by osmosis

Too little H2O: 1. Cl- pumped into cell across basal membrane

2.Cl- diffuses thru open CFTR channel 3.Na+ diffuses down electrical gradient into nucleus

4. Elevated salt conc. in mucus draws H20 out of cell by osmosis

5. H20 drawn into cell for mucus by osmosis

CFTR protein may be dysfuncfional or absent.

Too little H20, Cl ions can't be secreted across apical membrane ∴ no blockage of the epithelial Na ion channels.

Na+ channels always open, so continual Na+ absorption by epithelial cells (H20 lost a lot)

Raised levels of Na+ draw Cl ions and H20 out of mucus & into cells.--> Makes mucus more viscous ∴ harder for cilia to move it along.

Mucus not cleared up & out of lungs so clogs up airways and can lead to infection due to build up of bacteria.

Downward spiral of airway inflammation and damage.

1. CF and digestive system: Their pancreatic duct gets blocked by sticky mucus-> impairs release of digestive enzymes.

↓ conc. of digestive enzymes = ↓ rate of digestion.

Food not fully digested so not all nutrients absorbed & enegy lost in faeces.

^ Malabsorption syndrome ^

2. Can damage pancreas itself <--through trapped enzymes blocking duct.

CYSTIC FIBROSIS: Cysts of hard,damaged or fibrosed tissue in pancreas.

CF and reproductive system

Females lower chance of pregnancy-> mucus plug in cervix. Prevents sperm from reaching egg.

Males may lack sperm ducts (or blocked by mucus) so sperm can't leave testes or less reaches.

Globular proteins & biological CATALYSTS.

3D shaped enzyme has an active site <- specific shape to substrate being broken

Lock and key theory- Enzyme-Substrate Complex (ESC)

--Substrate forms temporary bond w/ amino acids of active site, producing an ESC

When reaction finished, products released & leave active site w/ enzyme unchanged.

Induced fit theory- active site flexible

Specific substrate induces change in shape of enzymes active site & fits closer to substrate.

Enzymes ↓ activation energy: electrically charged groups on surface interact

Attraction of oppositely charged groups can distort substrate, helping break it apart.

Higher enzyme:substrate ratio means more available active site to form ESC's.

Graphs, see pg 79.

CF occurs from mutation in DNA that carries instructions for making CFTR protein.

Code it contains are used to make proteins.

Watson and Crick: propsosed a model for structure of DNA (1953).

Gene: sequence of bases on a DNA molecule

^All genes in an individual/species known as genome

CF gene on chromosome 7.

>> instructs cell to make CFTR protein that forms the transmembrane chlorine channel.

Gene: A sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain.

DNA- polynucleotide (chain of nucleotides). Linked through condensation reactions.

DNA:1)Deoxyribose (5 carbon sugar) 2)Phosphate 3)Organic Base

DNA:1)sugars:Outside 2)Phosphates form "backbone" 3)Bases like rungs of a ladder.

Triplet code: (Three for variation instead of just 4 aa's)

Code carried by DNA is a (three-base) triplet code. -->Read down 3.

Every triplet code on DNA= complementary codon on mRNA

strand of RNA nucleotides. Contains ribose sugar. Uracil not Thymine in RNA

[Semi-conservative: Parts of Orignal used. Experiment with nitrogen- light medium and heavy DNA]

Transcription (in nucleus): (DNA POLYMERASE USED)

1) DNA unwinds & hydrogen bonds between bases break (strands partly separated)

2)Template strand (anti-sense) is used in production of mRNA

--complimentary base pairing means mRNA is exact reverse copy of DNA bit (but w/ U)

3)Free RNA nucleotides line up along template strand, join through CB pairing to form...

4) mRNA-moves out of nucleus & attaches to ribosome. See next card for 2nd stage.

5) When mRNA produced, hydrogen bonds between uncoiled strand of DNA reform.

Coils back into double helix

Translation (on ribosomes):

1)mRNA attaches itself to ribosome & tRNA molecules carry amino acids to ribosome

2) A tRNA molecule comes and attaches with CB to 1st triplet of bases (codon) on RNA.

3) 2nd tRNA molecule attaches itself to NEXT triplet on mRNA in same way

4) The two amino acids are joined together via peptide bond & 1st tRNA moves away, leaving amino acid behind. &.etc

5)Process continues, producing chain of linked amino acids (polypeptide chain)

Until stop signal on mRNA

Polypeptide chain moves away from ribosome and translation is complete

Cystic Fibrosis results from a number of possible gene mutations- can be due to errors in DNA replication.- Deletion of 3 nucleotides (most common)

mRNA altered which codes for a different protein.

Primary structure altered which changes the proteins final structure & function. Different bonds are formed. 2ndary folding and twisting alters.

Tertiary 3D folding is affected and final protein made is different.

Thalassaemia: Recessive allele, often lethal (-Haemo-), increase protection from malaria

Sickle cell anaemia: Mutation in gne that codes for a polypeptide chain in haemoglobin, H less soluble, half moon (sickle) carry less oxygen & can block bld vessels.

CF mutation: CFTR protein

Allele: different versions of same gene

Genotype: One's genetic make up

Phenotype: Observable effect due to genotype

Homozygous: 2 copies of same allele (FF)

Heterozygous: 2 different alleles (Ff)

Dominant: Affects phenotype if two or ven 1 present.

Recessive: Only affects phenotype if same allele present too.

Plasmid: Loop of DNA

Monohybrid cross

GT: Normal alleles inserted into target cells (either by virus or liposomes)

Normal form of gene transcribed & translated

Functioning protein produced in target cells. ->[In CF- CFTR protein produced restoring ion channel & avoids symptoms of CF.]

Via virus: 1. DNA sequence that allows virus to replicate is removed 2. Replaced with normal allele of desired gene 3. promoter sequence initiates transcription & translation.

viral DNA can: 1. Incorporate to cell's own DNA 2. remain independent in nucleus (CF)

BUT: inflammatory repsonse, headache, fatigue, raised HR

Via liposomes: 1. Normal allele inserted into plasmid 2. Plasmid combined with liposomes to form liposome-DNA complex 3. Patient breathes in complexes through nebuliser. Liposomes fuse w/ epithelial cell membranes & carry DNA into cells.

Genetic testing to: confirm diagnosis, identify carriers.

For testing embyros:

Amniocentesis: 1. Insert needle to get amniotic fluic containing foetal cells.

2. 15-17 weeks 3. 1% chance of miscarriage

Chorionic villus sampling (CVS): placental tissue with foetal cells removed either through abdominal wall or vagina. 8-12 wks, no need 4 amniotic fluid to develop. 2% of miscarriage

Pre-implantation genetic diagnosis: In IVF, test embryo before it has implanted in uterus. Cell removed from growing embryo & then analysed. Decide whether to put back in.

BUT: Expensive, can be unreliable- false positives

1. Rights and duties

2. Maximising amount of good in world

3. Being autonomous

4. Leading a virtuous life

Treatments for CF:

• Medication
• Diet
• Digestive enzyme supplements
• Physiotherapy
• Heart and lung transplant