Topic 2 - Proteins Flashcards
Lectures 6-8
What is the general structure of amino acids?
a-Carbon atom with 4 bonds to:
- hydrogen atom
- amino group
- carboxyl group
- R group
How many a-amino acids are commonly found in proteins?
20
What are common ways of categorizing R groups?
- Size
- Shape (aliphatic/aromatic)
- Hydrophobicity
- Charge
- Sulphur containing
- Imino acids
Which amino acids contain sulphur?
- Cysteine
- Methionine
Which alpha amino acid does not possess optical activity?
Glycine
Only which optical isomers are found in proteins?
L-isomers
levo-rotary
What are the properties of globular proteins?
- Compact
- Soluble (hydrophilic residues outside, hydrophobic hidden)
- eg. Enzymes, Haemoglobin
What are the properties of fibrous proteins?
- Elongated
- Often have repeating amino acid sequences
- Insoluble due to hydrophobic amino acid content
- eg. membrane proteins
What are the cellular functions of proteins?
- Structural
- Signalling
- Receptors
- Enzymes
- Binding
- Transporters
- Translation factors
What is the function of enzymes?
Lower the Ea of a reaction in order to catalyse metabolic reactions.
What factors restrict the number of combinations an amino acid chain could fold into?
- Rigidity of the peptide bond
- Physical and chemical properties of the side chains
Which proteins assist in protein folding?
Chaperone proteins
What are the two types of chaperone proteins?
Molecular chaperones - bind to long segments of protein to facilitate correct binding
Chaperonins - form folding chambers which provide a stable environment to encourage correct folding
What may happen when a protein is incorrectly folded?
- Cellular processes relying on the protein’s presence will stop (eg. cystic fibrosis, phenylketonuria)
- Misfolded protein may accumulate and hinder normal cellular processes (eg. Alzheimer’s)
- Misfolded protein may cause conformational changes in other proteins (eg. Creutzfelt-Jacob disease)
- Cell may identify the protein for early destruction
What is an amyloid disease?
e.g. Alzheimer’s diseases. Fragments of normal proteins produce amyloid fibrils.
What is a Prion disease?
e.g. Creutzfeldt-Jacob disease, BSE (mad cow disease) & scrapie (sheep & goats). An infectious protein agent causes a conformational change in a normal protein.
What are the signs of Alzheimer’s disease?
- memory loss
- loss of language ability
- loss of the ability to mentally manipulate visual information
- poor judgment
- confusion
- restlessness
- mood swings
- eventual death
What is the biochemical basis of Alzheimer’s?
- A fragment from a normal membrane protein, amyloid precursor protein, accumulates and aggregates forming insoluble fibrils of amyloid β protein in the brain.
- A fragment from a normal membrane protein, amyloid precursor protein, accumulates and aggregates forming insoluble fibrils of amyloid β protein in the brain.
- These plaques damage and destroy neurons.
What are the signs of Creutzfeldt Jacob Disease?
- Loss of neurological function
- Memory loss
- Loss of coordination and language ability
- Coma
- Eventual death
What is the infectious agent of Creutzfeldt Jacob?
Prion protein PrPSc
What is the biomedical basis of Creutzfeldt Jacob disease?
- PrPSc has an identical primary sequence to a normal membrane protein PrPc but has a much higher proportion of β-pleated sheet.
- Contact of normal soluble PrPc protein (mostly α-helical) with abnormal form PrPSc (mostly β-pleated sheet) causes the PrPc protein to acquire the abnormal PrPSc structure.
How many mutant Haemoglobins are known?
> 400
What is the function of myoglobin?
Oxygen STORE
