Cell Biology Unit 3 Lecture 2

Front 1

In which direction is RNA synthesized?

Back 1

In the 5'-3' direction, reading the DNA in the 3'-5' direction.

Front 2

What does RNA polymerase do?

Back 2

Responsible for transcription. Covalently adds ribonucleotides to the RNA strand.

Front 3

What determines which strand of DNA will be the template for transcription?

Back 3

A promoter.

Front 4

What is a transcriptional unit?

Back 4

Each transcribed segment of DNA.

Front 5

What is messenger RNA?

Back 5

Transcripts of protein-coding genes. 2-4% of total RNA. Short lived, degraded after synthesis.

Front 6

What is ribosomal RNA?

Back 6

Components of ribosome, most abundant RNAs, <80% of total.

Front 7

What is Transfer RNA?

Back 7

Involved in protein snythesis, carry amino acids to the ribosome.

Front 8

What are small nuclear RNA (snRNA)?

Back 8

Involved in mRNA processing.

Front 9

What are small nucleolar RNA (snoRNA)?

Back 9

play central role in the processing of rRNA

Front 10

What are small cytoplasmic RNA (scRNA)?

Back 10

diverse group with a range of functions.

Front 11

What are MicroRNAs (miRNAs)?

Back 11

family of 21-25 nucleotide small RNAs that negatively regulate gene expression at the post-transcriptional level.

Front 12

There are three RNA polymerases, what are they?

Back 12

RNA polymerase I- transcribes ribosomal RNA genes.
RNA polymerase II- transcribes protein coding and snRNA genes.
RNA polymerase III- transcribes tRNA and other short genes.

Front 13

How does a promoter work?

Back 13

The promoter contains DNA sequences that bind transcription initiation proteins. The TATA box is one such DNA sequence.

Front 14

What does RNA polymerase II require to assemble at the promoter?

Back 14

transcription factors- e.g. TBP, TFIIA, TFIIB, TFIID- Transcription Factors for RNA polymerase II.

Front 15

What do transcription factors do?

Back 15

Position recruit RNA polymerase II to the promoter and aid in RNA polymerase binding to the promoter.

Front 16

What are the steps of transcription?

Back 16

1. RNA polymerase and transcription factors assemble at the promoter.
2. The DNA is pulled apart. RNA polymerase is phosphorylated and undergoes a conformation change and released to begin transcription.
3. The new RNA transcript is released from the polymerase as it is synthesized, allowing RNA to be processed as soon as it is made.

Front 17

What are pre-mRNAs?

Back 17

Primary mRNA transcripts in the nucleus. They contain both intronic and exonic sequences. Processing includes 5' capping, addition of methyl-guanosine.

Front 18

What is polyadenylation?

Back 18

Addition of a polyA tail at 3' end. Directed by specific consensus sequences in the 3' end of RNA. Catalyzed by the polymerase enzyme.

Front 19

What is RNA splicing?

Back 19

The removal of introns. Specific consensus sequences in the pre-mRNA signal where splicing occurs. 5'donor site and 3' acceptor site (GU/AG rule). Alternative splicing gives rise to different proteins.

Front 20

What are the steps of pre-,RNA splicing?

Back 20

1. A specific adenine within the intron attacks the 5' splice site, cutting the sugar-phosphate backbone.
2. The cut 5' end of the intron covalently links to the adenine, creating a loop.
3. The free -OH group then reacts with the start of the next exon, joining the 2 exons. The intron in the shape of a lariat is released.

Front 21

What is a spliceosome?

Back 21

A group of snRNAs and small nuclear ribonucleo-proteins that perform RNA splicing.

Front 22

How do rRNAs, tRNAs, and mRNAs leave the nucleus and enter the cytoplasm?

Back 22

Exit via nuclear pore complexes that cover the nuclear membrane. RNA must be processed before leaving the nucleus.

Front 23

What is meant by degeneracy of the code?

Back 23

That there are 64 possible codons but only 20 amino acids.

Front 24

What is the initiation codon?

Back 24

AUG

Front 25

Which enzymes link a specific tRNA with a specific amino acid?

Back 25

aminoacyl-tRNA synthetases.

Front 26

Amino acids are added to which end of the protein?

Back 26

the C-terminus

Front 27

What is the wobble base?

Back 27

The 3rd position in codon not totally required to match by all tRNAs.

Front 28

What are the three major sites of action on a ribosome mRNA bonding site?

Back 28

P- peptidyl site
A- amino acyl tRNA site
E- exiting site

Front 29

What are the steps of initiation of translation?

Back 29

1. Initatiator tRNA is brought to the small ribosomal subunit with eIF-2 (eukaryotic initiator factors).
2. Initatiator tRNA can only bind without the large subunit attached.
3. mRNA transcript associates with eIF-4 at the 5'cap and 3' tail and is postioned in the small ribosomal subunit
4. Initatiator tRNA scans mRNA for AUG.

Front 30

What are the 4 steps of protein synthesis?

Back 30

1. aminoacyl-tRNA binds to a vacant A site.
2. A new peptide bond is formed at P site
3. The mRNA moves 3 nucleotide positions through the subunit to the E site.
4. The spent tRNA is ejected and the ribosome is reset.

Front 31

How is translation terminated?

Back 31

By the bonding of a release factor to an A-site bearing a stop codon. The protein is released and the ribosome dissociates.