BIO TOPIC 2 TO REMEMBER

Main symptoms of CF

(digestive system)

Impaired digestion

Damage to pancreas

Mucus blocks pancreatic duct & small intestine

Digestive enzymes cannot reach duodenum → reduced digestion of food + absorption of nutrients

Trapped digestive enzymes damage pancreatic tissue

Islets of Langerhans damaged → insulin production reduced/stopped → Type 1 Diabetes

Main symptoms of CF

(respiratory system)

lung infection

Breathing difficulties

Main symptoms of CF

(reproductive system)

Infertility

Women → mucus blocks cervix, delays puberty, pregnancy still possible

Men → Many do not have a sperm duct, if present its typically blocked by mucus, very few can reproduce naturally

Main symptoms of CF

(sweat )

Very salty sweat

No functional CFTR protein so Cl⁻ & Na⁺ are not reabsorbed and instead are lost in sweat

What's involved in the respiratory system

nasal cavity

nostrils

oral cavity

larynx

trachea

bronchus

lungs

bronchioles

alveoli

diaphragm

Goblet cells - adaptations + role

Produce mucus

Located between ciliated epithelia cells

Adaptations:

Large ER & Golgi

Many vesicles from which mucus is secreted out of cell

What is the role of mucus

To trap foreign particles (dust, bacteria) and remove them from entering the alveoli

Moisturises inhaled air

Type of epithelial cell & where they're located in the respiratory system (3)

Alveoli - simple squamous

Bronchioles - simple columnar

Trachea + Bronchi - Pseudostratified

Why do lung infections happen a lot

Mucus traps bacteria

Mucus is too sticky to be moved by cilia

Low O₂ levels in mucus, anaerobic bacteria thrive

WBC fighting bacteria die + release DNA making mucus stickier

Inflammation & infection

Mucus and breathing

Mucus blocks bronchioles

Less or no air reaches the alveoli

Reduced gas exchange

Diffusion

The movement of particles from an area of high concentration to an area of low concentration (down a concentration gradient) without using energy

Factors affecting diffusion

1. Concentration gradient

2. Surface area

3. Diffusion distance

4. Temperature

5. Size of molecule

Fick's law of diffusion

Rate of diffusion is inversely proportional to the thickness of the gas exchange surface

Why is gas exchange at alveoli efficient

Short diffusion distance - diffuses through 2 thin cells (epithelium & endothelium) to reach RBC + capillaries are one cell thick

Steep concentration gradient

Large surface area - many alveoli + they're really small → increases SA enormously

What is surfactant + role

Phospholipid

Prevents permanent collapse and sticking together of alveoli

How does build up of mucus in the bronchioles cause difficulties

Mucus blocks bronchioles → fewer alveoli available for gas exchange → reduce SA

Mucus fills alveoli → increased diffusion distance

Over-inflation of lungs tryna get enough O₂ → elasticity of lungs decrease → reduce gas exchange → O₂ shortage + tiredness

Zwitterions

In water at neutral pH, group are ionised

Dipeptide formation

Made via condensation reaction of two amino acids, form a peptide bond (amide bond), makes + removes a water molecule

Primary structure

The linear sequence of the amino acid in a protein

- contains a N terminus and a C terminus

Secondary structure

The regular folding of parts of a protein due to hydrogen bonds between peptide bonds

α helix

Forms a helix held by hydrogen bonds running PARALLEL with the long helical axis

Many hydrogen bonds makes it very stable & strong

β pleated sheet

Chain zig-zags back and forward forming a sheet of antiparallel strands

Strands held together by hydrogen bonds between peptide bonds

Tertiary structure

Overall 3-dimensional structure of the whole peptide chain, formed by bonds between R group

Hydrophobic interactions - between R groups

Hydrogen bonds - between H & O of R groups

Ionic bonds - between charged R groups

Disulphide bonds - covalent bonds between two cysteine R groups

Quaternary structure

3-dimensional structure of several polypeptide chains interacting with each other via bonds between R groups

Conjugated proteins

Proteins that joined to other non protein molecules (prosthetic groups

Globular proteins - properties + role

Compact + roughly spherical

Non-polar hydrophobic R groups are orientated towards the centre

Polar hydrophilic R groups orientate themselves on the outside of the protein

Some contain a prosthetic group

Physiological roles: enzymes, antibodies, hormones

Fibrous proteins - properties + role

Long, strong strands

Little to no 3° structure

Highly repetitive sequences - very organised structures

Structural roles: collagen & keratin

Haemoglobin - properties + role

4 polypeptide chains - 2x α -globin & 2x β - globin

Spherical, globular

Variable AA

Prosthetic - Haem group

Soluble in H₂O

Function - transporting O₂

Collagen - properties + role

3 polypeptide chains - triple helix

Long, thin, fibrous

Repetitive AA -every 3rd AA is glycine

No prosthetic group

Insoluble in H₂O

Function - connective tissue e.g. tendons, skin

Gorter and Grendel model - conclusion

Phospholipids form a bilayer

Gorter and Grendel model - evidence

Number of phospholipids extracted from red blood cell membranes = double the area of the plasma membrane if it was arranged as a monolayer

Gorter and Grendel model - problems

Did not explain the location of proteins or how insoluble molecules were moved in & out the cell

Davson and Danielli's model - conclusion

Proteins hold lipid bilayer in place & 'Protein lipid sandwich' model

Davson and Danielli's model - evidence

Membranes effective at controlling the movement of substances in & out of cells.

Electron micrographs showed the membrane had two dark lines with a lighter band between (In electron micrographs, proteins appear darker than phospholipids)

Davson and Danielli's model - problems

Freeze etched electron micrographs of the centre of the membrane showed globular structures scattered throughout.

Improvements in technology used to analyse the proteins in the membranes showed that proteins were globular, varied in size and had parts that were hydrophobic

Singer and Nicolson model - conclusion

FLUID MOSAIC MODEL

Lipids form two-dimensional liquid in which lipids can move (fluid)

Proteins attach to membrane some outside, some embedded within (mosaic)

Fluid

Two-dimensional 'liquid' with lateral movement of lipids and proteins through bilayer

Mosaic

Composed of different types of macromolecules

e.g. integral & peripheral proteins, lipids and glycolipids etc

Singer and Nicolson model - evidence

Analysis of freeze-etched electron micrographs showed proteins extending into the centre of membranes

Biochemical analysis of the plasma membrane components showed that membrane proteins are free to move within the bilayer

Phospholipid bilayer

Polar, hydrophilic, phosphate heads face towards solution

Non polar, hydrophobic lipid tail faces away from the solution

A bilayer forms with hydrophobic parts pointing in towards the centre of the bilayer/towards each other

Unsaturated fatty acids in the cell membrane

Causes the phospholipid to be less tightly packed

More movement possible

Role of cholesterol in the cell membrane

Regulates fluidity,

- prevents phospholipids from packing too closely together when temps low

- stabilises the cell membrane at higher temperatures

Role of glycolipids & glycoproteins

Markers for cell-to-cell recognition

Signalling

How do non polar molecules move through the membrane

Diffusion

Facilitated diffusion

Movement of molecules from an area where they are at a high concentration to an area where they are at low concentration via a carrier or channel protein

What are channel proteins used to transport

Polar molecules e.g. ions

What are carrier proteins used to transport

Larger molecules e.g. glucose or amino acids

Osmosis

Movement of water molecules from a high water potential to a low water potential across a selectively-permeable membrane

OR

Net movement of water into areas of high solute concentration across a selectively permeable membrane

Osmosis in animal cells

(using different solutions)

Hypotonic - solution with lower [solute] than cell / cell burst (lysed)

Isotonic - solution with same [solute] as cell / cell stays normal

Hypertonic - solution with greater [solute] than cell / cell shrivels

Osmosis in plant cells

(using different solutions)

Hypotonic - cell goes turgid

Isotonic - cell goes flaccid

Hypertonic - plasmolysed

Active transport

Movement of molecules from a low concentration to a high concentration via carrier proteins using energy from ATP

Exocytosis

Export of molecules out of cells involving vesicles that fuse with the cell membrane and release their contents

Endocytosis

Uptake of molecules by the creation of a vesicle from the cell membrane

What happens when there is too little water in the mucus of a healthy person

1. Cl⁻ is pumped into cell from tissue fluid across basal membrane

2. CFTR channel is open causing Na⁺ channel to close; Cl⁻ diffuses through the open CFTR channel

3. Na⁺ diffuses down the electrical gradient into mucus

4. High [salt] in mucus draws water out of the cells into mucus by osmosis: mucus becomes more runny

5. Water is drawn into cells from tissue fluid by osmosis

Why is mucus so sticky in cystic fibrosis

1) CFTR is absent or non-functional

2) Na⁺ channel is permanently open and Na+ diffuses into cells from mucus, and is pumped into tissue fluid

3) Cl⁻ diffuses out of mucus towards basal membrane via the intercellular space down an electrical gradient

4) Water is continually removed from mucus by osmosis; mucus becomes very sticky

5) Bacteria and WBC get trapped; DNA released from dead WBC makes mucus even more sticky

Lock and key theory

Substrate shape is complementary to shape of active site

Induced fit theory

Substrate binding induces shape change in active site which enables perfect fit and catalytic activity

Enzyme

Globular proteins that act as biological catalyst and speed up chemical reactions

They lower activation energy

What factors affect enzyme activity

Temperature

pH

[Substrate]

[Enzyme]

Inhibitors

Cofactors

Cofactors

Non-protein chemical compounds that are bound to enzymes and required for enzyme activity

Coenzyme - loosely bound cofactor (e.g. vitamin c, metal ions)

Prosthetic group - tightly bound cofactor (e.g. haem group)

Enzyme inhibitors

Competitive inhibitors - competes with substrate for active site ( can overcome by increasing [substrate] )

Non-competitive inhibitors - binds to allosteric site and changes shape of active site

Pyrimidines

1 carbon ring

Thymine & Cytosine

Purines

2 carbon rings

Adenine & Guanine ';

Facts about DNA

Codes for AA sequence in proteins

Deoxyribose sugar; A,C,G,T bases; double strand; very long

Located in nucleus

Constant amount in cells

Chemically very stable

Facts about RNA

mRNA (transcription); tRNA (translation)

Ribose sugar; A,C,G,U bases; single strand; shorter strands

Made in nucleus, found throughout cell

Varying amount in cells

Chemically unstable

Transcription

Copying of a length of DNA code one gene long into messenger RNA (mRNA)

- done in the nucleus

- catalysed by RNA polymerase

1.1 Transcription initiation (STEP 1)

1. RNA polymerase bind to DNA and scans for promoter region

2. RNA polymerase partially unwinds the DNA double helix

3. RNA polymerase starts to transcribe DNA sequence on the anti-sense strand into RNA sequence via complementary base pairing

Anti-sense strand transcribed

1.2 Transcription elongation

Transcription continues until the terminator is reached

1.3 Transcription termination

1. RNA polymerase reaches terminator

2. Transcription stops: RNA polymerase & RNA transcript are released

2.1 RNA processing

1. RNA transcript is spliced (introns, non-coding, are removed)

2. RNA transcript receives cap & tail

3. Processed RNA transcript = mRNA

3.1 mRNA export

mRNA is exported out of the nucleus via pore in the nuclear membrane

Translation process

1. Ribosome attaches to mRNA

2. Ribosome moves along mRNA (5' → 3') to find start codon

3. tRNA carrying specific AA w/ anticodons pairs up w/ codons (complimentary base pairing)

4. Next tRNA w/ anticodon complementary to next mRNA codon is loaded

5. Adjacent AAs joined via a peptide bond, catalysed by peptide synthetase

6. First tRNA is released

7. Elongation continues till stop codon reached

8. Release factor is loaded & translation stops

9. Polyprotein released

Nature of genetic code

Triplet code: 3 codons code for 1 AA

Degenerate: some AA's can be coded for by several codons

Universal: same code in all organisms

Non-overlapping: each codon is read separately

tRNA

Different tRNA for every codon

tRNA has anticodon sequence complementary to codon

tRNA binds to specific AA corresponding to anti-codon

Translation

Using the sequence of codons on mRNA to produce a sequence of amino acids in a protein

- occurs in cytoplasm

- catalysed by ribosomes, tRNA & peptide synthetase

Polysomes

Several ribosomes can bind to the same mRNA forming a polysome

- several polypeptide chains are made simultaneously

DNA replication

Copying of the entire genome in preparation for cell division

Steps of DNA replication

1. DNA helicase unwinds DNA double helix

2. The two strands of the DNA double helix are separated by breaking hydrogen bonds between base pairs

3. Parent strands act as template for new DNA strands, free nucleotides pair with the complimentary nucleotides, DNA polymerase forms phosphodiester bonds

4. Two identical new strands of DNA are made

5. Newly formed DNA rewinds into helices

Semi-conservative - context of DNA replication

One strand of the original parental DNA

One new DNA strand

Meselson-Stahl Experiment

Used isotope of nitrogen to change the weight of DNA N15 & N14, demonstrated that the semi-conservative model is the best description of replication.

FIX

Point mutation

A point mutation is a change in a single nucleotide (base)

Types of frameshift mutations

Deletion & Insertion

- very serious causing a different AA sequence to be produced

Type of silent mutation

Substitution

- less serious due to degenerate code

Type of missense mutations

Substitution & Inversion

- changes AA sequence

Type of nonsense mutation

Substitution

- stop codon produces a truncated protein

Mutations in CFTR gene

Almost 1400 different mutations

In 70% of cases ΔF508 mutation

mutation ΔF508 is a deletion of three nucleotides, its a missense (not frameshift because 3 codons are removed not just one) causing the AA sequence change

Gene

A sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chain

Allele

A variation of a gene

Genotype

The alleles present

Phenotype

The characteristics resulting form expression of the genotype

Recessive

An allele that is only present in the absence of a dominant allele / when homozygous

Dominant

An allele that is always expressed in the phenotype

Incomplete dominance

When the trait from a dominant allele is not completely expressed over the trait produced by the recessive allele

Homozygote

Having identical alleles on homologous chromosomes

Heterozygote

Having different alleles on homologous chromosomes v

Genetic testing (carrier testing)

Tested to see if it contains the most common mutation for a particular genetic disease

Samples of cheek cells or WBC tested

- 80% to 85% reliable

Preimplantation Genetic Diagnosis (PGD)

Fertilisation by IVF

A cell is removed from the resulting embryos at the 8-16 cell stage

The DNA is analysed

Prenatal screening - amniocentesis

During pregnancy (15-18 weeks or later)

Needle used to remove foetal cells from amniotic fluid

DNA is analysed

Prenatal screening - amniocentesis

(ADV vs DIS)

ADV:

1% risk of miscarriage

Results available in 3 days (NHS)

DIS

Only carried out later in pregnancy

Risk of a false positive upon which decisions including abortions could be made

Prenatal screening - chorionic villi sampling

During pregnancy from 10 weeks onwards (NHS 2019)

Suction tube used to remove foetal cells from chorion

DNA is analysed