Proteins And Their Functions Flashcards
Stop codons ?
UAA
UGA
UAG
Start codon?
AUG
Codes for aa methionine
What structure requires the lowest energy
Tertiary
Homomer quaternary structure
Made from same polypeptide chain
Heteromer quaternary structure
Different polypeptide chains
Technologies used to look at protein structure in fine detail
- X-ray crystallography
- Nuclear magnetic resonance
- Cryo-EM
Are proteins rigid structures?
No. Conformation is dynamic.
Induced fit hypothesis
Regulation of proteins (4 steps)
- Synthesis
- Localisation
- Modification
- Degradation
When may synthesis of proteins occur? Examples
- immune response
- differentiation
- in response to signalling
What directs a protein to a desired organelle
Sorting signal
3 methods of protein transport
Nuclear pores
Across membranes
Transport by vesicles - RER to Golgi appa to final organelle
Secretory pathway?
Proteins transported between compartments via transport vesicles
Specialised cells have secretory vesicles which store hormones and enzymes for future use
Types of secretion (2)
o Constitutive secretion:
unregulated
secretion occurs continuously no external signals required
o Regulated secretion:
requires extracellular signal
Difference between secretory and transport vesicles
Secretory contain materials that are to be excreted from the cell
Transport move molecules within the cell
Protein modification?
• Most proteins are post translationally modified in the endoplasmic reticulum (rER)
• Includes disulphide bonds and glycosylation (i.e. sugars added)
• Further modified in the Golgi apparatus
Regulation of proteins?
- Phosphorylation. Phosphate attached covalently to aa side chains.
Can inhibit or activate protein
Induces conformational change
What protein catalyses phosphorylation
Protein kinase
Protein that catalyses dephosphorylation
Protein phosphatase
What is the unfolded protein response?
Homeostatic response
Excessive accumulation of misfolded proteins triggers response
Expands ER enabling proper folding
If ER cannot cope then translation inhibited and apoptosis
Example of UPR?
DIABETES
Insulin resistance. More insulin produced to compensate and ER reaches max capacity
Cytoplasmic signalling
Adapter protein binds to phosphorylated receptor
And Ras G protein then binds to adaptor protein.
Growth factor signalling
Tyrosine kinase receptor becomes activated by GF
Leads to phosphorylation an d dimerisation of the receptor
Degradation of proteins ?
Misfolded/damaged proteins are transported to lysosomes & endosomes for degradation
Three stop codons
UAG
UAA
UGA
What does every protein sequence start with
Met amino acid
What is a sorting signal
A signal which causes a newly manufactured protein from the RER to move to the correct site in a cell via transporters
What makes proteins so diverse
Variation in side chains of the proteins
What is the synthesis of proteins
Ribosomes are responsible for the synthesis of proteins. Proteins destined for intracellular use are produced in free ribosomes, whereas proteins for extracellular export are produced in the rER. These processes are regulated.
What is protein localisation
It is important that proteins get to where they are needed. Proteins have a sorting signal which allows them to be moved in transport vesicles to their correct destination. They can be taken into organelles via protein transporters
What is protein modification
Proteins are modified in the ER and golgi apparatus. Modifications involve glycolysation (adding stability) and phosphorylation (conformational change) among others. Kinases are involved in phosphorylation. This is a regulated process.
What is protein degradation
Proteins are folded in the ER. The ER is responsible for the homeostatic control of the balance between folding and endoplasmic reticulum associated degradation (ERAD) . If too many unfolded proteins are produced, it produces a signal which inhibits further production of that protein. This is a regulated process.
