Lecture 23 - Exam III

How is hair color controlled? How does hair turn grey?

Melanocyte stem cells in hair follicles receive signals to become mature cells that make the protein pigments responsible for hair color. These cells are continuously multiplying and move between growth compartments in hair follicles- these get stuck as people age, and they can no longer receive the hair color signals.

What is the name of the largest gene in the human genome?

Dystrophin gene; 99.5% of gene is intronic

What is the Gilbert hypothesis?

Genes arose as collections of introns were pieced together to form functional exons. Also: exon shuffling (introns may speed up evolution by promoting genetic recombination between exons- hot spots for new combinations of exons and, thus, the formation of new genes)

The collagen triple helix consists of a repeating _ sequence

(Glycine - X- Y)n

Collagen has the pulling pressure/UTS comparable to:

Wood

What evidence is there that perhaps introns and exons are purposefully positioned?

Pyruvate kinase gene- each exon encodes a discrete secondary structural element, and introns define where primary structure makes a reverse turn

What are functional nuclear introns?

Accomodate sequences important for the expression of the gene in which the intron resies

What is miRNA? What is unique about where its gene can be found?

Important for translation of mRNA to protein; intermediary between DNA and proteins. Genes may be found on introns

Nuclear introns can be important in _

Alternative splicing - producing multiple distinct mRNAs from a single gene

What is the “c-value” ?

The total amount of DNA in the haploid genome

What is the c-value paradox?

There is no clear correlation between the size of a genome and the number of functional genes

It is likely that the size of a genome and the number of functional genes it has is impacted by:

the amount of retrotransposon DNA collected in the genome

What is a retrotransposon?

Transcribe DNA into RNA then use reverse transcriptase to make DNA copy of RNA to insert into a new location

Why does it make sense that proteins, rather than genes, are responsible for our complexity?

* Proteins are made up of 20 modifiable AAs while DNA is made up of 4 unmodifiable base pairs
* There are more distinct proteins in the human body than genes

Are proteins static? If not, how may they be modified (examples)?

Phosphorylated, sulfated, glycosylated, avetylated, ubiquitinated, ADP-ribosylated

Are genes dynamic/changing?

May be methylated (i.e. epigenetics)

Does protein synthesis occur on the rough or the smooth ER?

Rough ER

What is the function of the smooth ER? (SER)

Cholesterol metabolism / membrane synthesis / detoxification / Ca+ storage

What is the function of the rough ER?

Protein synthesis! Ribosomes are bound to the cytosolic side of the membrane

What are three types of ribonucleoproteins?

1. Ribosomes
2. Telomeres
3. Spliceosomes

What is the proportion of protein vs. RNA in a ribosome?

2/3 RNA, 1/3 protein

* Name of the e. Coli ribosome
* Dissociate in _ mM Mg2+
* What are the subunits and their number of proteins and components?
* Which subunit is larger?
* What percent of an e. Coli cell’s mass is ribosome?

1. 70S
2. 1
3. 30S - 21 proteins and 16S rRNA / 50S - 33 proteins and 23S rRNA, 5S rRNA
4. 50S subunit is larger
5. 20%

What are polyribosomes?

a group of ribosomes bound to an mRNA molecule like “beads” on a “thread.” Found in both prokaryotes and eukaryotes

What is the third binding site within an e. Coli ribosome?

E site (“exit site”): Outgoing/unloaded tRNA sits here momentarily before dissociating

In e. Coli, which ribosomal subunit binds to mRNA first?

30S

The initiator tRNA in prokaryotes is:

formylated methionine: tRNAfMet (formylated by formyl transferase, tetrahydrofolate)

What happens to the formylated methionine added to the beginning of all e. Coli proteins?

Cleaved off in most proteins - peptide deformylase leaves normal methionine behind; methionine aminopeptidase removes the whole formylated methionine residue from the peptide chain

What are the components of the 30S initiation complex?

Initiation factor proteins, GTP, N-formyl-Met-tRNA, mRNA, and 30S ribosomal subunit

Correct “registration” during initiation in prokaryotes requires:

alignment of a pyrimidine-rich sequence on the 3’ end of the 16S rRNA with the purine-rich (As and Gs) SD sequence on mRNA

Chloramphenicol, linomycin, puromycin, and tetracycline are _ and cause _

antibiotics / premature chain termination during translation

Tetracycline, and streptomycin are _ and cause _

Antibiotics / interfere with binding of the aminoacyl tRNA to the acceptor site

Spectinomycin is _ and causes _

Antibiotic / interferes with initiation and elongation steps of translation