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Alex's Genetics > Lecture 11b > Flashcards

Lecture 11b Flashcards

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Biology 101 flashcards
1
Q

What is the start codon? What amino acid does it code for?

A

AUG, which codes for Methiony.

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2
Q

What are the stop codons? What do they cause?

A

UAA, UGA, UAG. These stop protein synthesis.

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3
Q

What type of bond connects the codon to the anticodon?

A

Hydrogen bonding

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4
Q

Which of the 3 RNA polymerases makes tRNA?

A

RNA polymerase III

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5
Q

Before we have our mature tRNA, what does RNA pol III first produce? What has to happen to it?

A

RNA pol III first makes a longer RNA that has extensive base-pairing. Then, enzymes will come along and cleave a lot of it, producing the mature tRNA.

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6
Q

What is RNase P?

A

A ribozyme that is comprised of both protein and RNA. The RNA performs the catalytic activity.

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7
Q

What performs the catalytic activity: RNA or protein?

A

RNA has the catalytic activity, the protein is just helping.

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8
Q

What is an endonuclease?

A

An enzyme that cleaves nucleic acid at an internal site.

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9
Q

What is an exonuclease?

A

An enzymes that cleaves from one end up until a point.

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10
Q

What is the shape of the tRNA produced after cleaving? How long is it?

A

It has a clover-leaf shape and is about 76 nucleotides folded up.

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11
Q

What is different about the mature tRNA from the precursor tRNA?

A

There are lots of nucleotide modifications in the mature tRNA.

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12
Q

What is the acceptor stem in the tRNA?

A

This is an area of the tRNA where there is an end jutting out and this is where the amino acid will bind.

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13
Q

What are the weird letter combinations showing in the mature tRNA here?

A

This is showing the modifications in the nucleotides in the mature tRNA.

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14
Q

What is special about this part of the tRNA?

A

The length can vary here from short to long.

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15
Q

What are aminoacyl-tRNA synthases?

A

They are enzymes/ribosomes that use ATP to attach amino acids to acceptor stems.

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16
Q

Describe the process of attaching ATP to tRNA acceptor stems.

A

1) An amino acid and adenine-monophosphate (AMP) are inserted into the cavities of the aminoacyl-tRNA synthase. AMP is covalently bound to the amino acid.
2) The correct tRNA binds to the enzyme.
3) The covalent bond between AMP and the amino acid is transferred to the tRNA and amino acid. Thus, the amino acid is now covalently bound to the tRNA.
4) The “charged” tRNA now leaves the enzyme.

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17
Q

What is a charged tRNA?

A

When a tRNA has an amino acid bound to it.

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18
Q

How many amino acids and how many aminoacyl-tRNA synthetases are there? Why is this important?

A

There is 1 aminoacyl-tRNA synthetase for every 1 amino acid.

Thus, there are 20 aminoacyl-tRNA synthetases and 20 amino acids. This gives us specificity for proteins.

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19
Q

What is a ribosome?

A

A huge enzyme where translation (protein synthesis) takes place.

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20
Q

What is a polypeptide?

A

A chain of amino acids that are hanging off of the tRNA in protein synthesis.

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21
Q

T/F: The large and small ribosome subunits are stuck together permanently.

A

False! These can separate from each other.

22
Q

What is always the first amino acid to attach during protein synthesis?

A

Methiony (Met)

23
Q

T/F: Many proteins will contain the Met amino acid after protein synthesis.

A

False. While Met is the first amino acid to start protein synthesis, it is often removed at the end.

24
Q

What gathers at the start codon to initiate eukaryotic translation?

A

The small and large units of the ribosome, mRNA, and charged tRNA with the Met amino acid all assemble at the start codon.

25
Q

What is the Peptidyl (P) site?

A

This is where the tRNA and mRNA hydrogen bond. Several amino acids will be attached to the tRNA that is present here with the exception of the very start of protein synthesis.

26
Q

How do amino acids attach to each other during protein synthesis?

A

The first amino acid in the P site is transferred to the second amino acid. This is happening at the same time that the second amino acid tRNA is being moved from the A to the P site. The tRNA in the P site is also moved to the E site to be ejected.

27
Q

What is the Aminoacyl (A) site?

A

This is where the “next” tRNA with an amino acid will sit before it moves to the P site. Only tRNAs with a SINGLE amino acid will be in this site.

28
Q

What is the Exit (E) site?

A

This is where tRNAs that have just given their amino acid away will be ejected out of.

29
Q

What is a peptide bond?

A

The bond between two amino acids.

30
Q

What occurs at termination of protein synthesis?

A

Elongation of the polypeptide chain occurs until a stop codon is reached. A protein called a release factor enters the A site and everything falls apart so that the polypeptide chain is released.

31
Q

When does the Release Factor fit into the A site?

A

It only fits into the A site when you have a stop codon.

32
Q

For bacteria, where does transcription and translation occur? Why is this?

A

Transcription and translation occur in the cytoplasm. This occurs because bacteria do NOT have a nucleus.

33
Q

For eukaryotes, where do transcription and translation occur?

A

Transcription occurs in the nucleus at the nucleoplasm.

RNA is then transported out of the nuclear pores into the cytoplasm.

Translation occurs in the cytoplasm.

34
Q

How is protein synthesis different in bacteria?

A

Ribosomes are synthesizing proteins as RNA polymerase is producing the RNA.

35
Q

What is a Polysome?

A

In bacteria, this is when a bunch of ribosomes are moving along the mRNA and making proteins.

36
Q

What is this a picture of?

A

This is a picture of protein synthesis occurring in bacteria.

37
Q

What are the 4 main identifiable structures in polypeptides?

A

1) Amino terminal end (N terminus)
2) Backbone of the polypeptide chain
3) R Groups/Side Chains
4) Carboxyl terminal end

38
Q

What is the Amino terminal end / N terminus?

A

This is the side of the polypeptide made from the 5’ end of the mRNA. Here, the nitrogen on the end has only Hydrogens attached to it.

39
Q

What is the backbone of the polypeptide chain? State the sequence.

A

This is where each of the amino acids in the chain has a section that looks the same. The sequence is N, C, C double bonded to O.

40
Q

What are R groups / Side chains?

A

These are the structures that hang off of the middle carbon in the backbone. This is what differs between amino acids.

41
Q

What is the carboxyl terminal end?

A

This is the end of the polypeptide chain that is synthesized by the 3’ end. This is where we will add incoming amino acids and get water as a result. We can distinguish this end by looking for an O hanging off of the carbon that is not the double-bonded O.

42
Q

T/F: For each amino acid, there is only one codon.

A

False. For many amino acids, there can be multiple codons.

43
Q

What is the most codons an amino acid can have?

A

The most is 6 codons per 1 amino acid.

44
Q

What is the ribosome used in translation?

A

It is a ribozyme, NOT a protein.

45
Q

How many RNA polymerases do Eukaryotes have?

A

3

46
Q

What does RNA polymerase I do?

A

It produces the RNA to make a ribosome, except for 5S rRNA.

47
Q

What RNA polymerase makes 5S rRNA?

A

RNA polymerase III, which also makes tRNA.

48
Q

What is catalysis done by? How do we know this?

A

Catalysis is done by RNA. We know this because people stripped away 80% of the proteins and the ribosome was still able to function.

49
Q

What were proteins originally synthesized by?

A

RNA

50
Q

What did people realize when self-splicing was discovered?

A

People realized that RNA had preceded proteins in evolution. This means that RNA was present in the world first, then came proteins, and last came DNA.

Thus, RNA must recruit proteins.

Alex's Genetics (38 decks)

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