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BIO 221 01 > CH_11 > Flashcards

CH_11 Flashcards

To learn and retain information from CH 11 from the course Cell Biology

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1
Q

Transcription

A

The process by which an RNA is synthesized from a DNA template in the nucleus

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2
Q

Translation

A

The process by which proteins are synthesized from an mRNA template in the cytoplasm

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3
Q

Messenger RNA (mRNA)

A

An intermediate between a gene (DNA) and a polypeptide (Protein)

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4
Q

What are mRNA assembled as?

A

A complementary copy of one of the two DNA strands that make up the gene

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5
Q

Fucntions of mRNA

A

Allows the cell to separate information storage from information utilization

Allows a cell to greatly amplify

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6
Q

What are RNA polymerase responsible for?

A

Transcription in both prokaryotes and eukaryotes

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7
Q

What are RNA polymerase capable of doing?

A

Incorporate nucleotides one at a time, into a strand of RNA from a DNA template

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8
Q

What do RNA polymerase require the help of?

A

Require the help of transcription factors to recognize the promter

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9
Q

What does the RNA polymerase bind the DNA template to?

A

The promoter

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10
Q

What is a promoter?

A

A region of DNA that locates prior to the transcription start site of a gene

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11
Q

What are the functions of the promoter?

A
  1. Contains information that determines which of the two DNA strands will be used as the template and where transcription will begin
  2. Initiates transcription
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12
Q

What direction does the newly synthesized RNA chain grow?

A

5’ to 3’ direction, antiparallel to the DNA template

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13
Q

What does the RNA polymerase establish during transcription?

A

The transcription bubble

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14
Q

What happens to the DNA after RNA polymerase passes?

A

DNA double helix re-forms

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15
Q

What happens to newly synthesized RNA ?

A

It dissociates with DNA template

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16
Q

How long is the DNA-RNA hybird?

A

About 9 base pairs long

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17
Q

What are properties of RNA polymerase?

A

RNA polymerase must be processiv–remain attached to DNA over long stretches

RNA polymerase must be able to move from nucleotide to nucleotide.

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18
Q

What are Ribonucleoside triphosphates substrates (NTPs) cleaved to?

A

Nucleoside monophosphates as tthey are polymerized into RNA chain

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19
Q

What rule are NTPs incorporated to?

A

The Watson-Crick base pairing rule

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20
Q

How many RNA polymerase are in prokaryotes?

A

One

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21
Q

Composed of _____ subunits named as the _______________

A

five, core enzyme

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22
Q

Where does the core enzyme bind?

A

It binds randomly

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23
Q

What does the sigma factor do?

A

Biding to the core enzyme to facilitate interaction with DNA at specific promoter sites

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24
Q

What RNA polymerase is used in eukaryotes?

A

RNA polymerase II

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25
Q

What is needed to recognize the promoter?

A

Transcription factors

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26
Q

What is the name for the initially synthesized RNA

A

Primary transcript

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27
Q

What will the primary transcript be processed to become?

A

Mature RNA or mRNA

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28
Q

What is a transcription unit?

A

The DNA segment corresponding to a primary transcript

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29
Q

What are properties of mRNA

A

They each code for a specific polypeptide

They are found in the cytoplasm

They are attached to ribosomes when translated

Most have a noncoding segment

Eukaryotic mRNAs possess specific modifications at their 5’ and 3’ end
5’: methylated guanosine cap
3’: poly(A) tail, composed of 50-250 adenosine residues

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30
Q

Function of the 5’ cap

A

Prevents the 5’-end of mRNA from being digested by enzymes

Aids in transport of the mRNA out of the nucleus

Plays an important role in the initiation of translation

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31
Q

Function of the 3’ poly (A) tails

A

All mRNAs possess a string of adenosines (50-250) at their 3’end

Protect the mRNA from premature degradation by enzymes

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32
Q

What synthesizes all eukaryotic mRNA precursors?

A

RNA polymerase in the nuclues

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33
Q

What does RNA polymerase associate with?

A

General transcription factors (GTFs) to form the preinitation complex (PIC)

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34
Q

What does the PIC assemble?

A

The critical portion of the promoter, it lies 24-32 bases upstream (5’ - 3’) to the iniation site and its called the TATA box (5’- TATAAA- 3’)

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35
Q

What does the TFIIH do?

A

Possess enzymatic activites

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36
Q

What does the protein kinase do?

A

Phosphorylate RNA polymerase II

37
Q

What does the helicase?

A

Unwinding DNA double helix to generate the transcription bubble

38
Q

What is an Exon?

A

Parts contribute to the mature RNA

39
Q

What is an Intron?

A

Intervening sequences, which are excluded from the mature RNA

40
Q

How are Pre-mRNA transcripts processed?

A

Cotranscriptionally

41
Q

What happens to RNA transcripts as they are synthesized?

A

They be come associated with ribonucleoproteins

42
Q

What happens to RNA transcripts as they are processed?

A

A 5’ methyguanosine cap and 3’ poly (A) tail are added

43
Q

What happens to the introns and exons?

A

Introns are removed and exons are connected by RNA splicing

44
Q

What is RNA splicing?

A

A modification process of the nascent pre-messenger RNA (pre-mRNA) transcript in which introns are removed and exons are joined to produce the mRNA

45
Q

What are splice sites?

A

Jucntions between introns and exons

46
Q

What is GU?

A

The 5’ splice site of intron

47
Q

What is AG?

A

The 3’ splice site

48
Q

What tracts near the 3’ splice site?

A

Polypyrimidine

49
Q

Where do splice sites get assistance from?

A

Exon splicing enhancers (ESEs) situated in the exon

50
Q

Is Pre-mRNA self-splicing?

A

No they require help from small nuclear RNAs (snRNAs) and their associated proteins

51
Q

What does the intron become associated with?

A

A complex called spliceosome

52
Q

What is the splicesome consisted of?

A

The spliceosome consists of small nuclearribonucleoproteins(snRNPs)

  • snRNA + specific proteins
  • U1, U2, U5, and U4/U6 snRNPsare required
53
Q

What is Alternative splicing?

A

A regulated process during gene expression that results in a gene coding for multiple proteins

54
Q

How is information stored in a gene?

A

Stored in a gene in the form of a genetic code, named codons

55
Q

What are the properties of codons?

A

Triplets of nucleotides

non-overlapping

Degenerate
o some of the amino acids are specified by more than one codon

56
Q

Do the first two codon bases for an amino acid change?

A

No, the first two are invariant, whereas the thrid may vary

57
Q

How are codons for specicfic and smilar amino acids?

A

They tend to be clustered

58
Q

What are the types of nucleotide mutations?

A

Synonymous- does change the amino acid sequence

Non-synonymous- causes an amino acid substitution

Nonsense- creates a premature termination codon

59
Q

How many nucleotides does an insertion or deletion mutation add/ delete?

A

One or more

60
Q

What is a frameshift DNA mutation?

A

Alters the normal reading frame of the mRNA

61
Q

What is the role of tRNA?

A

tRNA translate a sequence of mRNA codons into a sequence of amino acid residues

62
Q

What does tRNA transfer?

A

Appropriate amino acid to specific codons

63
Q

What is the length of tRNAs?

A

73 to 93 nucleotides

64
Q

What is the structure of tRNA?

A

All tRNAhad a significant percentage of unusual bases

All tRNAs have sequences of nucleotides in one part of the molecule complementary to sequences located in other part of the same molecule, forming stem of the cloverleaf

All mature tRNAs ended in CCA at their 3’ end

65
Q

What is an Anticodon?

A

A stretch of three sequential nucleotides reisde in tRNA that decode codon information through formation of complementary base pairs between codons on mRNA transcript

66
Q

What is the wobble hypothesis?

A

A tRNA can recognize codons with variable third bases

3rd position: U with A or G (codon); G with U or C (codon); I with U, C, or A (codon)

67
Q

What do aminoacyl-tRNA synthetases (aaRS) do?

A

Link amino acids with their respective tRNAs

68
Q

How aaRS exist?

A

There are 20 different that exist in an organism

69
Q

What is the small and large ribosomal subunit?

A

40S and 60S

70
Q

What is the purpose of Ribosomal RNAs (rRNA)?

A

Structural support

Catalyze the chemical reaction in which amino acids are covalently linked to one another

71
Q

What is the purpose of Transfer RNAs (tRNA)

A

Required to translate the information in the mRNA nucleotide code into the amino acid

72
Q

How many binding sites to tRNA have?

A

3 binding tRNA binding sites:
A (aminoacyl) site
P (peptidyl) site
E (exit) site

73
Q

What is the 1st Step of Translation?

A

43S complex binds to the 5’ end of mRNA complex and scan for the AUG start codon

74
Q

What are the components of 43S complex?

A

Ribosomal 40S subunit

Initiator tRNAlinked to a methionine

eIFs: eIF2-GTP

75
Q

What are the components of mRNA complex?

A

mRNA

eIF4E: binding to 5’-cap

eIF4A: remove double stranded structure

eIF4G: linked 5’ and 3’ end

76
Q

What is the 2nd Step of Translation?

A

Large subunit (60S) joins the complex after 43S complex reaches the appropriate AUG codon

77
Q

What happens after the 2nd Step of Translation?

A

Complete assemble of 80S ribosome

All eIFsare released

Initiator tRNAbinds to the P site of the ribosome

78
Q

What are the properties of elongation?

A

The elongation cycle is the process of adding each subsequent amino acid to the growing polypeptide chain.

Specific proteins will be required, referred as “elongation factors(eEFs)”

2 GTPs are required for each cycle of elongation

79
Q

What are the major steps of elongation?

A

Step_1: Aminoacyl-tRNAselection
Step_2: Peptide bond formation
Step_3:Translocation
Step_4: Releasing the deacylatedtRNA

80
Q

What happens during the first step of elongation: Aminoacyl-tRNA selection

A

With the charged amino acid in the P site, the next aminoacyl-tRNAbinds to the vacant A site is the first step for elongation

Any aminoacyl-tRNAcan enter the A site, but ONLY the one with complementary anticodon can trigger the conformational change of ribosome

81
Q

What happens during the second step of elongation: Peptide bond formation

A

Catalyzed by peptidyl transferase

Amine nitrogen of the amino acid bound to the A site tRNAlinked to carboxyl carbon of the amino acid bound to the P site tRNAfor the formation of peptide bond

Result in a dipeptide bound to the tRNAat A site, and tRNAat P site is deacylated

82
Q

What happens during the third step of elongation: Translocation

A

Translocation refers to the procedure that ribosome moves three nucleotides (one codon) in the 5’ to 3’ direction on the mRNA molecule

Accompanied with the movement of:

  • The dipeptidyl-tRNAfrom the A site to the P site of the ribosome
  • Deacylated tRNA from the P site to the E site
83
Q

What happens during the fourth step of elongation: Releasing the deacylated tRNA

A

The deacylatedtRNAleaves the ribosome and empty the E site of the ribosome

84
Q

What three stop codons cause termination?

A

UAA, UAG, or UGA

85
Q

What does termination require?

A

Release factors, which recognize stop codons

86
Q

What type of release factor do eukaryotic cells have?

A

eRF1, they recognize all the stop codons

87
Q

What does termination accompany?

A

Accompanied by dissociation of the mRNA from the ribosome and the disassembly of the ribosome

88
Q

What is a polyribosome?

A

A polyribosome (or polysome) is a complex of mulitple ribosomes on mRNA, allowing simultaneous translation, they increase the rate of protein synthesis

BIO 221 01 (11 decks)

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