Cell Bio - Unit 2 - Transcription/translation

Front 1

What is the central dogma?

Back 1

The flow of genetic information in cells is from DNA to RNA to protein

Front 2

T or F:
Many identical RNA copies can be made from the same gene.

Back 2

True

Front 3

Name this process:
Each RNA molecule can be translated to many identical protein molecules.

Back 3

Amplification

Front 4

T or F:
Expression of genes UN-regulated.

Back 4

False

Front 5

What are the three steps of protein production for Eukaryotes?

Back 5

Transcription, processing and translation.

Front 6

Fact: RNA is single stranded which allows it to fold into a variety of complex 3-D shapes, enabling it to carry variety of functions in cells.
What stabilizes these shapes?

Back 6

Complementary base pairing.

Front 7

List the functions of RNA (6 listed in the notes).

Back 7

mRNA, tRNA, rRNA, Catalytic structures, Primer in DNA replication, Genetic information in some viruses.

Front 8

Name the molecule that does the following:
*Catalyzes the addition of a 5'-ribonucleoside triphosphateto the 3'-end of the RNA-transcript.
*Unwinds the DNA in front of itself as it advances along DNA double helix.
*Rewinds the DNA after it is transcribed

Back 8

RNA polymerase

Front 9

Y/N: Does RNA polymerase require a primer?

Back 9

No

Front 10

RNA polymerase attaches to DNA at ____ _____, which consists of a specific base sequence that is unique for each type of RNA polymerase.

Back 10

Promoter sites

Front 11

Define and describe: Stop (Termination) Signal.

Back 11

DNA base sequence that causes the RNA polymerase to detach from the DNA.
*Consists of a self-complimentary sequence followed by a region of poly-A bases.

Front 12

Describe the two steps involved in processing mRNA during transcription?

Back 12

1. Capping of 5'-end
*Addition of 7-methyl guanosine to the 5'-end of the transcript.
*Cap attached by an unusual 5'-5' triphosphate bond.
*Capping occurs soon after the 5'-end (the front end) of the transcript emerges from the RNA polymerase.

2. Polyadenylation
*An enzyme cuts the transcript at a specific sequence and removes part of the 3'-end of the transcript after it is released from the RNA polymerase.
*A second enzyme attaches multiple adenine nucleotides to the 3'-end of the transcript(poly-A "tail").

Front 13

95% of mRNA consists of introns (noncoding sequences) which are removed by _____.

Back 13

Splicing

Front 14

snRNPs (snRNAs + proteins) recognize specific RNA base sequences and form spliceosomes which remove ____.

Back 14

introns.

Front 15

What is the intermediate form that introns assume during the splicing process of pre-mRNA?

Back 15

Lariat

Front 16

After protein synthesis, what degrades mRNA molecules in the cytosol?

Back 16

Nucleases

Front 17

Fact: There are 61 codons, including 1 start codon and 3 stop codons.
What is the start codon?

Back 17

AUG - methionine

Front 18

What all is required for transcription to occur?
*There are 7 listed in the notes

Back 18

*mRNA
*ribosomes - small subunit and large subunit
*tRNA's
*amino acids
*protein "factors"
-initiation factors
-elongation factors
-release factor
*Energy source - GTP, ATP
*Enzymes

Front 19

Where do amino acids attach to on the tRNA molecule?

What kind of bond occurs?

Back 19

-3'-OH end
-aminoacyl bond (Aminoacyl-tRNA)

Front 20

What enzyme assures that the correct amino acid is attached to the proper tRNA?

Back 20

Aminoacyl-tRNA Synthetase

Front 21

What are the 2 types of ribosomes?

Back 21

Procaryotic and eucaryotic

Front 22

Fact: In eucaryotes tRNA subunits are made in the nucleus (by association of rRNAs with ribosomal proteins transported from cytoplasm) and exported to cytoplasm.
Describe the 2 subunits of tRNA.

Back 22

Small Subunit - matches the incoming tRNAs to the codons of the mRNA
Large Subunit - catalyzes the formation of the polypeptide bonds that link amino acids into a polypeptide chain.

Front 23

What is another name for catalytic RNAs?

Back 23

Ribozymes

Front 24

Describe the 4 binding sites of a ribosome.

Back 24

*mRNA binding site
*A-site
aminoacyl-tRNA binding site, holds an incoming tRNA with attached amino acid
*P-site
peptidyl-tRNA binding site, holds a tRNA attached to the growing polypeptide
*E-site
exit site, briefly and loosely holds the departing tRNA before it is released into the cytosol.

Front 25

List the steps involved in translation initiation.
*There are 6 listed in the notes.

Back 25

*Initiator tRNA-Met attaches to initiation factors (IF).
*IF-Met-tRNA complex attaches to the P-site of a small ribosomal subunit.
*small ribosomal subunit attaches to the 5'-end of an mRNA and slides along it until the tRNA-Met anticodon recognizes an AUG codon and stops.
*IF's dissociate.
*large subunit binds to mRNA and small subunit.
*next aminoacyl tRNA enters the A site ~ chain elongation begins.

Front 26

What determines the rate of protein synthesis?

Back 26

Initiation

Front 27

Describe the 3 steps involved in chain elongation.

Back 27

*Binding of an aminoacyl-tRNA to the vacant A-site
*Detachment of the carboxyl-end of the peptide attached to the tRNA in the P-site and reattachment, via a peptide bond, to the amino-end of the amino acid attached to the tRNA in the A-site. This central reaction of protein synthesis is catalyzed by *peptidyl transferase.*
*Translocation of the new peptidyl-tRNA from the A-site to the P-site shifts the ribosome three bases along the mRNA. Moving a new codon into the A-site requires energy.

Front 28

When does termination occur?

Back 28

When one of three stop codons enters the A-site on the ribosome.

Front 29

Describe the 3 steps involved in termination.

Back 29

*Release factor protein enters the A-site and binds to the stop codon
*Peptidyl transferase catalyzes the addition of water to the carboxyl end of the peptide attached to the tRNA in the P-site, releasing the peptide.
*Ribosome detaches from mRNA and dissociates into its two subunits.

Front 30

What is it called when multiple ribosomes are attached to a single mRNA?

Back 30

Polyribosome (polysome)
-Free in the cytosol or attached to ER

Front 31

What are the differences in Procaryotic and Eucaryotic translation?

Back 31

Procaryotes:
*no 5'-cap
*Specific ribosome-binding sequence precedes the start codon.
*Initiator tRNA carries formylmethionine.
*May be more than one start codon -more than one polypeptide per mRNA = polycistronic message.

Eucaryotes:
*Addition of 7-methyl guanosine cap to the 5'-end of the  transcript aids recognition by the small ribosomal subunit.
*Only one start codon per mRNA = monocistronic message.

Front 32

List and Describe the drugs that inhibit protein synthesis in Procaryotes and Eucaryotes.

Back 32

Procaryote-specific (antibiotics):
Tetracycline - blocks binding of aminoacyl-tRNA to A-site of ribosome.
Streptomycin - prevents transition from initiation complex to chain-elongating ribosome.
Erythromycin - blocks the translocation reaction on ribosome
Chloramphenicol - blocks the peptidyl transferase reaction on ribosome.

Eucaryote-specific
Cycloheximide - acts on translocation step, produced by Streptomyces Griseus, used in research only.

Act on both procaryotes and eucaryotes:
Puromycin - causes premature chain termination, product of Streptomyces Alboniger, used in research only.
Actinomycin D - transcription inhibitor, first isolated antibiotic, old chemotherapeutic drug.

Front 33

Define Proteolysis.

Back 33

Proteins are degraded by proteases in enzymatic reactions.

Front 34

Proteins broken down in cytosol by large complexes of proteolytic enzymes, aka ______, are marked for destruction by covalent binding of small proteins called _____.

Back 34

-proteasomes
-ubiquitins