| Question |
Answer |
| Two strategies for generating an abundance of rRNA |
Includes multiple copies of rRNA genes
Multiple transcripts to be simultaneously produced from each gene.
|
| Oscar Miller feathers |
Multiple transcripts look like the barbs of a feather |
| Nucleolus |
Region of a nucleus where ribosomes are produced.
NOT a membrane bound organelle.
|
| Each gene encodes how many rRNAs? |
3 |
| What transcribes rRNA |
Pol I |
| Pre-rRNA |
One large RNA molecule transcribed by Pol I |
| What transcribes a fourth rRNA? |
A separate 5SrRNA gene. |
| What transcribes the fourth rRNA? |
Pol III |
| Ribonucleoproteins |
Proteins that assemble around the rRNA to form the large and small subunits of ribosomes. |
| What composes ribosomes? |
RNA and protein |
| What are the post transcriptional modifications of tRNA? |
Intron splicing
Nucleotide addition
Methylation
Modifications to produce unusual nucleotides
|
| How many loops do tRNA have? |
3 |
| What are the 3 loops of tRNA? |
D loop
Anticodon Loop
TψCG Loop
|
| Folding of tRNA |
Internal annealing folds tRNA into “clover leaves” |
| What genes make up the small subunit? |
18S |
| What genes make up the large subunit? |
5.8S, 5S, 28S |
| What is the secondary fold of tRNA? |
The D and TψCG Loops fold back on each other to generate an L shaped structure |
| Unique properties of RNA polymerase I and Pol III promoters |
Unlike Pol II, promoters for rR?NA and tR?NA lack TATA boxes |
| Where are mRNA, tRNA and ribosomes produced? |
Nucleus |
| Where does translation occur? |
cytoplasm |
| How do components get imported and exported from the nucleus? |
nuclear pore complexes |
| What are nuclear pore complexes? |
channels embedded in the nuclear envelope. |
| How many different proteins make up nuclear pore complexes? |
30 |
| What are the proteins that make up nuclear pore complexes called? |
nucleoporins |
| What mediates transport of factors into or out of the nucleus? |
importins and exportins |
| What happens to tRNA when it gets to cytoplasm? |
It becomes charged |
| Are tRNA ready for translation in the nucleus? Why? |
No. They must be charged in the cytoplasm |
| What enzyme charges tRNA? |
aminoacyl-tRNA synthetase |
| What makes tRNA charged? |
Binding to an amino acid |
| Where does tRNA bind to amino acids? |
3' OH of tRNA binds with carboxyl group of the amino acid. |
| Does charging of tRNA require ATP? |
yes |
| Can amino acids be bound to several tRNAs? |
yes
|
| Can tRNAs be bound to different amino acids? |
NO. Only one tRNA can be bound to an amino acid. |
| How can the cell use only four nucleotides to code for twenty different amino acids? |
Every 3 bases in mRNA codes for a different amino acid. |
| Codon |
a nucleotide triplet that specifies a particular amino acid |
| Characteristics of the Genetic Code (7) |
Triplet
unambiguous
Degenerate
Wobble
Colinear
Non-overlapping
Universal |
| Triplet |
every three bases of mRNA sequence, read 5' - 3' |
| Unambiguous |
codons only specify one amino acid |
| Wobble |
The thrid base of codons that specify the same amino acid varies. The first two are usually identical |
| What is the start cdon? |
AUG |
| What amino acid is the start codon |
Methionine codon |
| All polypeptides begin with |
Methionine (Met) Codon |
| What does the ribosome look for when it grabs mRNA? |
It reads down the length in the 5' - 3' direction looking for the AUG triplet.
It begins to add amino acids to teh grwoing polypeptide chain at this point. |
| Stop codons |
UAA
UAG
UGA |
| When will the ribosome stop growing the polypeptide chain? |
When it gets to a stop codon |
| Polypeptide |
a polymer of amino acids. |
| Peptide bond |
Carboxyl moiety of one amino acid is bound to the amino moiety of the next |
| Residue |
an amino acid in the sequence of a polypeptide |
| directions |
during translation the RNA is read 5' - 3' while the polypeptide is synthesiszed from the amino to carboxyl ends |
| What are the 3 stages of the translation pathway? |
Initiation
Elongation
Release |
| Initiation stage |
Ribosomes are assembled with an mRNA between the large and small subunits, along with the first aminoacyl tRNA (Met). This tRNA is bound to the P site of teh ribosome. |
| Elongation Stage |
Addition of amino acids to the growing polypeptide chain |
| Peptidyl site |
P site.
a region of the ribosome that binds the tRNA that is attached to the growing polypeptide |
| Aminoacyl site |
A site.
a region of the ribosome that binds that aminoacyl tRNA for the next amino acid to be bound to teh growing polypeptide. |
| Release Stage |
the completed polypeptide, mRNA and both ribosomal subunits all come apart |
| What is protein sorting? |
proteins are targeted to specific cellular compartments such as mitochondria, chloroplasts, peroxisomes or rER |
| 5 Principle types of Post translational modification |
disulfide bond formation
glycosylation
cleavage
polypeptide forlding
multisubunit assembly |
| Where does Post translational modification occur? |
ER |
| What is glycosylation? |
addition of carbohydrate side chains |
| Where does glycosylation occur? |
Golgi |
| Where does cleavage occur? |
Golgi and vesicles |
| What mediates proper folding? |
helper protiens known as chaperons |
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