Biology

Gases e.g. oxygen cross walls if alveoli into blood by diffusion.

Features of a good gas exchange surface:

• Large surface area of alveoli
• Lots of capillaries around alveoli
• Thin walls of alveoli and capillaries ao there is short distance between alveolar air and blood in capillaries

Rate of diffusion in body depends on:

• Surface Area - as surface area increases, so does rate of diffusion
• Concentration Gradient - greater the concentration gradient faster the diffusion
• Thickness of gas exchange surface - thicker the surface, slower the diffusion

Positive phosphate head - hydrophilic

Negative phosphate tail - hydrophobic

Bilayer arranges itself so the hydrophilic heads are facing out to the water and hydrophobic tails are on the inside of the two layers.

Fluid Mosaic Model
Fluid - proteins free to move around
Mosaic - some molecules in fixed patterned arrangement

Diffusion

• Molecules moving from a region of high concentration to low concentration
• Small molecules diffuse easily across membranes
• No energy required. Concentration gradient is maintained

Facilitated Diffusion

• Molecules passing through bilayer through water filled pores in channel proteins
• Some proteins in facilitated diffusion are carrier proteins that bind to specific sites on proteins then change shape so they can pass through
• Sometimes called passive transport
• No energy required

Osmosis

• Movement of water molecules from low concentration of solute molecules to an area of high concentration of solute molecules

Active Transport

• Substances moving across a membrane from low to high concentration - requires energy
• Specific carrier proteins also needed
• Energy come from respiration, supplied by energy transfer molecule ATP
• Energy from ATP changes shape of carrier protein causing substance to be released on other side of membrane

Exocytosis & Endocytosis

• Exocytosis is release of substances from cell as vesicles (small memrane bound sacs. Endocytosis is reverse process

Excess Water

• Sodium pumped across basal membrane
• Sodium diffuses through sodium channels in apical membrane
• Chlorine diffuses down electrical gradient
• Water drawn out of cells by osmosis due to high salt concentration in tissue fluid
• Water drawn out of mucus by osmosis

Too Little Water

• Chlorine pumped into cell across basal membrane
• Chlorine diffuses through  open CFTR channels
• Sodium diffuses down electrical gradient into mucus
• Elevated salt concentration in mucus draws water out if cell by osmosis
• Water drawn into cell by osmosis

With CF

• CFTR channel absent or not functional
• Sodium channel permanently open
• Water continually removed from mucus by osmosis

deoxyribonucleic acid

Made up of:                Arranged in mononucleotides

Phosphate       Deoxyribose sugar        Organic base

There are 4 bases - adenine (A), cytosine (C), guanine (G) and thymine (T)
paired up A-T (2 H bonds), C-G (3 H bonds)

DNA in chromosomes carries genetic information from one generation to next.

RNA made by copying the DNA (ribonucleic acid). Which leaves nucleus carrying information to cytoplasm where it manufactures proteins. 
RNA only has single strand of nucleotides that contain ribose sugar not deoxyribose. 

1. Transcription

• Double helix unwinds (helicase)
• RNA produced involving enzymes
• Completed RNA molecule leaves nucleus through pore and enters cytoplasm

2. Translation

• Takes place on ribosomes
• tRNA molecule carrying amino acids has 3 bases called anticodon which pairs with complementary bases on mRNA codon
• Amino acids carried by tRNA join by peptide bonds

Medication:
- Bronchodilators -  relax muscles in airways relieving tightness in chest
- Antibiotics - kill/prevent growth of bacteria in lungs
- DNAase enzymes - break down DNA so mucus is easier to clear from lungs
- Steroids - reduce inflammation to lungs

Diet:
- Recommended high energy foods
- Double quantity of protein
- Some may also need salt supplements 

Digestive enzyme supplement:
- Helps to complete digestion as in CF pancreatic duct is blocked

Physiotherapy:
- Rhythmical tapping on walls of chest loosen mucus and improve air flow
- Carried out twice a day

Heart & Lung Transplant: Only if lungs become inefficient. Last resort treatment. 

1. Normal alleles of gene inserted into target cells using genetically modified virus or liposomes

2. Normal form of gene is transcribed and translated

3. Functioning protein produced in target cells

Testing on embyos:

Chronic villus sampling:

• sample of placental tissue removed
• can be carried out earlier between 8-12 weeks - no need to wait for amniotic fluid to develop
• caries risk about 1% to 2% miscarriage
• gives chance to decide upon abortion early in pregnancy - physicaly and emotionally easier for mother

Testing before implantation:

• pre-implantation gene diagnosis (PIGD)
• in IVF, remove cell from embryo growing in culture
• DNA of cell analysed to be decided whether embryo to be placed in womb
• expensive and unreliable procedure