Get 1 week of unlimited access
Class Notes (1,036,486)
US (406,926)
UCLA (11,942)
MCD BIO (199)
arispe (32)
Lecture 15

MCD BIO 165A Lecture 15: lecture 15 POST-TRANSLATIONAL MODIFICATIONSPremium

7 pages45 viewsFall 2018

Department
Molecular, Cell, and Developmental Biology
Course Code
MCD BIO 165A
Professor
arispe
Lecture
15

This preview shows pages 1-2. to view the full 7 pages of the document.
Lec 15
POST-TRANSLATIONAL MODIFICATIONS
Longevity & biological responses has nothing to do with number of chromosomes
Number of chromosome has no direct correlation with number of genes
Size of genome has no direct correlation from those two
Why is size of genome bigger while number of genes is smaller?
- Long non-coding DNA, junk DNA
We share 92% gene with mouse, 98% with chimp, 44% with Drosophila
- Similar homologues & function -> model organisms
When analyzing an organism’s complexity: what other than the count of genes needs to
be considered?
- Same gene gives a variety of proteins thru splicing
How are distinct proteins generated from low number of genes?
- generation of different mRNA transcripts from a single gene
Genomic recombination
Differential transcription initiation sites
Differential transcription termination
Alternative splicing
- Post-translational modifications of proteins
Proteome complexity can be upped x5 compared to # of genes
Post-translational modifications (PTM) increases functional diversity of proteome by:
- Covalent addition of functional groups or proteins
- Proteolytic cleavage of regulatory subunits
Post-translational modifications (PTM)
Occur at distinct amino acid side chains or peptide linkages and are mediated by
enzymatic activity
Estimated that 5% of proteome comprises enzymes that perform more than 200 types of
PTMs
Includes:
- Kinases
- Phosphatases
- Transferases
- Ligases (e.g. addition of ubiquitin)
add or remove functional groups, proteins, lipids or sugars to or from aa chains
chemical specificity: e.g. phosphate can only be added to Tyr, Thr, Ser
“active/inactive”; allows protein function that was previously not possible
Some can be reversible (e.g. phosphorylation)
Biologically active insulin requires PTMs
- In most cases protein made in a zymogen state (inactive protein)
Zymogen: inactive form of protein; only activated when cleaved
Prefix “prepro”: a certain amount of amino acids not present in mature protein
You're Reading a Preview

Unlock to view full version

Subscribers Only

Only half of the first page are available for preview. Some parts have been intentionally blurred.

Subscribers Only
E.g. collagen made as preprocollagen; has to be proteolyzed to make final
collagen molecule
Important: removal of peptides inhibit association of fibers, don’t want to have
fiber formation inside cell -> need to build system where fiber formation only
occurs after fibers secreted outside cell
Prepro form allows cell processing of molecule in absence of polymerization
Another e.g.: insulin
- Before PTM: preproinsulin
- 24aa removed by signal peptidases -> proinsulin
Occurs co-translationally (as protein poured into ER)
- Proinsulin travels in ER & gets to Golgi
- Protein folded in Golgi; disulfide bridges connect amino & carboxy region (A & B
chains)
- Region in between (C peptide) removed in Golgi -> final insulin
If run insulin in SDS-PAGE: have 2 peptides (but coming from the same
polypeptide template)
- All these cleavages are critical parts of post-translational modification essential for
generation of mature hormone
Most common PTMs:
You're Reading a Preview

Unlock to view full version

Subscribers Only

Loved by over 2.2 million students

Over 90% improved by at least one letter grade.