Translation

0.0(0)
studied byStudied by 0 people
learnLearn
examPractice Test
spaced repetitionSpaced Repetition
heart puzzleMatch
flashcardsFlashcards
Card Sorting

1/51

encourage image

There's no tags or description

Looks like no tags are added yet.

Study Analytics
Name
Mastery
Learn
Test
Matching
Spaced

No study sessions yet.

52 Terms

1
New cards

What reads the mRNA to put together the amino acid chain?

2
New cards

Other than protection, what else can the 7-methyl-guanosine cap do?

Facilitate the transport of mRNA out of the nucleus in eukaryotic cells.

3
New cards

How many genes can prokaryotes express on a transcript? Contrast with eukaryotes. What is the term for this?

In eukaryotic cells, there is one mRNA for one gene. In prokaryotic cells, up to 10 genes sharing one mRNA; such an mRNA is called polycistronic.

4
New cards

How many codons are there for the various amino acids?

5
New cards

What is the start codon?

AUG, which specifies methionine

6
New cards

What is always the first amino acid? Why?

Methionine, because AUG is always the start codon and it is the only codon that codes for methionine.

7
New cards

What are the stop codons?

UAA, UAG, UGA; signal to the ribosome to release the mRNA

8
New cards

What is meant by redundancy in this case?

- The genetic code can have more than 1 codon to specify many of the Amino Acids

- Exceptions: Methionine and Tryptophan

- We use the term "wobble" for redundancy

9
New cards

What are the four steps in translation?

Amino acid activation; chain initiation; chain elongation; chain termination

10
New cards

What is "activation"?

The amino acid is attached to the transfer RNA that is used in the process of translation.

11
New cards

What is an anticodon?

An anticodon is the three unpaired bases on a tRNA that is complementary to one mRNA codon.

12
New cards

What happens at the A, P, and E sites of the ribosome?

tRNAs enter in the A site, progress to the P site, and exit in the E site. The single exception is the very first tRNA, which enters the P site.

13
New cards

Where does the mRNA go? Where does the tRNA go?

mRNA binds to the small ribosomal subunit, and tRNA goes to the large ribosomal subunit

14
New cards

Why does the first tRNA go directly to the P site?

-The first tRNA, methionine binds before the large subunit comes in, so the only one available is the P site

15
New cards

What is the structure of ribosomes?

2 subunits: Large and small

16
New cards

What is the structure of the tRNA? Where does the amino acid attach? Where is the anticodon loop?

The tRNA has a cloverleaf structure. At one end of the tRNA is an anticodon loop. The 3' end of the anticodon loop ends in CAA; this is where the amino acid attaches.

17
New cards

What does the enzyme family aminoacyl tRNA synthetases do? How many are there?

There are 20 aminoacyl tRNA synthetases, one for each amino acid. They read anticodons and attach the proper amino acid to the 3' end. Each enzyme can read as many anticodons as there are for a given amino acid.

18
New cards

How soon can translation begin in prokaryotes? Contrast with eukaryotes.

In prokaryotes, at the same time as transcription, because ribosomes are present in the cytoplasm.

19
New cards

What organisms have formyl-methionine (fmet)?

Prokaryotes have this modified form of methionine. Attachment of the formyl group occurs while the methionine is on the tRNA.

20
New cards

What is "wobble"? How does it work? Why is it useful?

Some anticodons use inosine at the 5' end, as a "wobble" base, meaning it gives the cell flexibility in that I will base-pair with A, C, or U. If the cell uses I in the wobble position of the tRNA, it can use that tRNA for several purposes.

21
New cards

What is a ribosome made of?

rRNA and proteins

22
New cards

What determines the naming of ribosomes?

Their sedimentation coefficients. (depends on their mass and shape)

- S = Svedberg Unit

Prokaryotes:

Small: 30S

Large: 50S

Complete = 70s

Eukaryotes

Small: 40S

Large: 60S

Complete = 80s

23
New cards

How is the growing polypeptide chain made?

Translation proceeds in the 5' to 3' direction along a mRNA.

Incoming tRNAs enter the ribosome and add their amino acids one at a time. The ribosome moves along the mRNA one codon at a time, facilitated by the protein EFG.

24
New cards

What is elongation factor G?

The protein that facilitates the movement of the ribosome along mRNA.

25
New cards

Where would we find a Shine-Dalgarno sequence? What does it match to?

8-10 nucleotides, mostly purines, upstream of the start codon, the AUG that is actually meant as a start signal and as an internal methionine. Only prokaryotes have this.

26
New cards

How do cells know if an AUG is intended to be a start codon or an internal methionine?

Presence of a Shine-Delgarno sequence 8-10 nucleotides upstream.

27
New cards

What are initiation factors? What kind of proteins are they?

The initiation phase of protein synthesis in prokaryotes begins with the binding of the mRNA by the small subunit of the ribosome. Initiation factors are proteins that help this occur. They are G proteins; they bind guanosine nucleotides and use their energy for activity. They use the Shine-Delgarno sequence as their orientation mechanism.

28
New cards

What molecule provides nearly all the energy for translation?

GTP

29
New cards

What does EF-Tu do? Is has several jobs.

EF-Tu (EF = elongation factor) carries tRNA to the A site of the ribosome and protects it during transport; the covalent bonding between the tRNA and the AA at the 2' end is very unstable in water. EF-Tu also performs quality control, making sure the correct base pairing occurs between the anticodon and the codon in the A site

30
New cards

How is the peptide bond formed? What enzyme does it?

The bond is made by the 23S ribosomal RNA, a ribozyme

31
New cards

What is a ribozyme? What does its existence support?

A ribozyme is a catalytic RNA. All peptide bonds form as a result of ribozymes. The fact that a nucleic acid can act as an enzyme supports theories of how early life formed.

32
New cards

How does termination occur?

When a stop codon appears in site A, the ribosome pauses because there is no tRNA that is complementary to that sequence. A release factor comes to the A site, bringing a water molecule to break the bond at the P site between the polypeptide chain and the tRNA. The polypeptide chain is released and the two subunits of the ribosome come apart.

33
New cards

How is the last bond broken (tRNA-polypeptide chain)?

a water molecule

34
New cards

Contrast eukaryotic and prokaryotic translation.

EUKARYOTIC DIFFERENCES:

- mRNA structured differently (have a cap and a tail)

- Ribosomes are different sizes (60S and 40S)

- Extra rRNA

- No Shine-Dalgarno

- No fMet

35
New cards

What is the purpose of a Kozak sequence?

Similar to the Shine-Delgarno sequence in prokaryotes, a Kozak sequence in eukaryotes helps determine what AUG that appears in the sequence is the right one to use as a start site. In eukaryotic cells, the first AUG that appears in the sequence is usually the right one.

36
New cards

What is the purpose of elF4E?

In eukaryotic translational initiation, eIF4E is the protein that binds the 7-methyl guanosine cap.

37
New cards

What does the eukaryotic initiation complex do?

- Brings the poly-A tail into close proximity of the start site so that when termination happens and the small subunits and the large subunits come apart, they don't have to travel very far to get to the AUG. Probably helps the ribosome find the AUG.

38
New cards

What are small RNAs? What are some of their roles?

- A type of RNA.

- Help to control gene expression

- "flag" a mRNA for destruction by RISC

39
New cards

What are some ways to get a lot of use out of an mRNA?

Make a stable mRNA with a longer half-life

40
New cards

How do cells carefully control their protein levels? How many ways can you think of?

Controlling mRNA abundance

41
New cards

What does RISC do?

Mediates gene expression by cutting and degrading mRNA.

42
New cards

What is post-transcriptional modification?

The process in eukaryotic cells where primary transcript RNA is converted into mature RNA.

43
New cards

What are some examples?

5' cap of modified guanine; the poly-A tail on the 3' end; splicing; RNA editing, which is alteration of nucleotide sequences within the RNA molecule, potentially changing the encoded amino acid sequence.

44
New cards

What happens to the newly translated polypeptide chain?

Some undergo folding in the rough ER, and/or modification by attachment of special groups (sugars/lipids/phosphates) in the Golgi apparatus

45
New cards

How can the cells in one organism all contain the same genome but turn into very different cell types?

Regulatory mechanisms that result in selective gene expression.

46
New cards

How does the trp operon function via feedback inhibition?

5 genes coding for 3 enzymes necessary to the production of tryptophan are encoded on the trp operon. Tryptophan binds to the inactive form of the trp operon's repressor, trpR, activating it. Repressor activation is concentration-dependent.

47
New cards

How can histones be used for gene silencing?

Genes bound to histones can't be expressed.

48
New cards

How is this changed?

Genes become accessible if histones undergo acetylation, methylation, or phosphorylation, which decreases the histone's affinity for DNA.

49
New cards

What does a transcription factor do?

Binds to the promoter region of DNA and acts to enhance or repress transcription

50
New cards

Why is an AT-rich region easier to pull apart?

1 fewer H bond than a C-G pair

51
New cards

What is an enhancer? Is it part of the gene?

- Interact with activators.

- When activators bind to the enhancer, another protein can bend to bring the activators closer to the promotor.

52
New cards

Can you name several regulatory strategies to control gene expression?

Some genes can only be transcribed when specific activator proteins are present. Acetylation/deactylation of histones to make genes accessible or inaccessible. Proteins that bind to mRNA to prevent translation.