Chapter Eleven Transcription of the Genetic Code: The Biosynthesis of RNA - PowerPoint PPT Presentation

1 / 52
About This Presentation
Title:

Chapter Eleven Transcription of the Genetic Code: The Biosynthesis of RNA

Description:

Chapter Eleven Transcription of the Genetic Code: The Biosynthesis of RNA * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Eukaryotic ... – PowerPoint PPT presentation

Number of Views:112
Avg rating:3.0/5.0
Slides: 53
Provided by: LauraM172
Category:

less

Transcript and Presenter's Notes

Title: Chapter Eleven Transcription of the Genetic Code: The Biosynthesis of RNA


1
Chapter ElevenTranscription of the Genetic Code
The Biosynthesis of RNA
2
Transcription
  • Overview of Transcription
  • synthesized on a DNA template, catalyzed by
    DNA-dependent RNA polymerase
  • ATP, GTP, CTP, and UTP are required, as is Mg2
  • no RNA primer is required
  • the RNA chain is synthesized in the 5 -gt 3
    direction the nucleotide at the 5 end of the
    chain retains its triphosphate (ppp) group
  • the DNA base sequence contains signals for
    initiation and termination of RNA synthesis the
    enzyme binds to and moves along the DNA template
    in the 3 -gt 5 direction
  • the DNA template is unchanged

3
Transcription in Prokaryotes
  • E. coli RNA Polymerase
  • molecular weight about ______________________
  • four different types of subunits
    _____________________
  • the _____________ enzyme is ?2??
  • the _____________ is ?2??s
  • the role of the s subunit is recognition of the
    ______________ the s subunit is released after
    ________________
  • of the two DNA strands, the one that serves as
    the template for RNA synthesis is called the
    template strand or ____________ strand the other
    is called the coding (or nontemplate) strand or
    _____________ strand
  • the __________ binds to and transcribes only the
    ___________

4
The Basics of Transcription
5
Promoter Sequence
  • Simplest of organisms contain a lot of DNA that
    is __________________________
  • RNA polymerase needs to know which strand is
    _____________strand, which part to _____________,
    and where first _____________ of gene to be
    transcribed is
  • _____________ - DNA sequence that provide
    direction for RNA polymerase

6
Promoter Sequence
7
Chain Initiation
  • First phase of transcription is _____________
  • _____________begins when RNA polymerase binds to
    _____________and forms ________________ complex
  • After this, DNA unwinds at _____________ to form
    open complex, required for chain ____________

8
Initiation and Elongation in Transcription
9
Chain Elongation
  • After strands separated, transcription
    _____________ of 17 bp moves down the DNA
    sequence to be transcribed
  • RNA polymerase catalyzes formation of
    _____________bonds between the incorporated
    _____________
  • Topoisomerases _____________ _____________ in
    front of behind __________ bubble __________

10
Chain Elongation (Contd)
11
Chain Termination
  • Two types of termination mechanisms
  • 1. intrinsic termination- controlled by specific
    sequences called _____________ _____________,
    characterized by two _____________ _____________

12
Chain Termination (Contd)
  • 2. Other type of termination involves rho (?)
    protein
  • ?-dependent termination sequences cause hairpin
    loop to form

13
Transcription Regulation in Prokaryotes
  • In prokaryotes, transcription regulated by
  • __________________________________
  • __________________________________
  • __________________________________
  • __________________________________
  • Alternative s factors
  • ___________ ____________ exert control over
    which genes are expressed by producing different
    s-subunits that direct the RNA _____________ to
    different genes.

14
Control by Different ? Subunits
15
Enhancers
  • Certain genes include sequences upstream of
    ____________________________________
  • These genes for ribosomal production have _____
    upstream sites, _________ sites
  • Class of DNA sequences that do this are called
    ______________
  • Bound by proteins called _________ _________

16
Elements of a Bacterial Promoter
17
Operon
  • _________ a group of operator, promoter, and
    structural genes that codes for proteins
  • the control sites, promoter, and operator genes
    are physically adjacent to the structural gene in
    the DNA
  • the regulatory gene can be quite far from the
    operon
  • operons are usually not transcribed all the time
  • __________________, an inducible protein
  • coded for by a structural gene, _________
  • structural gene _________ codes for lactose
    permease
  • structural gene _________ codes for
    transacetylase
  • expression of these 3 structural genes is
    controlled by the regulatory gene ______ that
    codes for a repressor

18
How Does Repression Work
  • Repressor protein made by lacI gene forms
    tetramer when it is translated
  • Repressor protein then binds to operator portion
    of operon
  • Operator and promoter together are the control
    sites

19
Binding Sites On the lac operon
  • Lac operon is induced when E. coli has _________
    as the carbon source
  • Lac protein synthesis repressed by ____________
    (catabolite repression)
  • E. coli recognizes presence of glucose by
    promoter as it has 2 regions RNA polymerase
    binding site, _________ _________ _________ (CAP)
    binding site

20
Binding Sites On lac operon (Contd)
21
Catabolite Repression
  • CAP forms complex with _________
  • Complex binds at CAP site
  • RNA polymerase binds at available binding site,
    and _____________ occurs

22
Basic Control Mechanisms in Gene Control
  • Control may be _________ or _________, and these
    may be _________ or _________ controlled

23
Control of the trp operon
  • Trp operon codes for a leader sequence (trpL) 5
    polypeptides
  • The 5 proteins make up 4 different enzymes that
    catalyze the multistep process that converts
    chorisimate to tryptophan

24
Alternative 2 structures can form in trp operon
  • These structures can form in the leader sequence
  • Pause structure- binding between regions 1 and 2
  • Terminator loop- binding between regions 3 and 4
  • Antiterminator structure- Alternative binding
    between regions 2 and 3

25
Attenuation in the trp operon
  • Pause structure forms when ribosome passes over
    Trp codons when Trp levels are high
  • Ribosome stalls at the Trp codon when trp levels
    are low and antiterminator loop forms

26
Transcription in Eukaryotes
  • Three RNA polymerases are known each transcribes
    a different set of genes and recognizes a
    _____________________________________
  • RNA Polymerase I- found in the _________ and
    synthesizes precursors of most _________
  • RNA Polymerase II- found in the _________ and
    synthesizes _________ precursors
  • RNA Polymerase III- found in the _________ and
    synthesizes _________, other RNA molecules
    involved in mRNA _________ and _________ _________

27
RNA Polymerase II
  • Most studied of the polymerases
  • Consists of 12 subunits
  • ______ - RNA Polymerase B

28
How does Pol II Recognize the Correct DNA?
  • 4 elements of the Pol II promoter allow for this
    phenomenon

29
Initiation of Transcription
  • Any protein regulator of transcription that is
    not itself a subunit of Pol II is a _________
    _________
  • Initiation begins by forming a _________
    _________
  • Transcription control is based here

30
General Transcription Initiation Factors
31
Transcription Order of Events
  • Less is known about _________ than _________
  • The phosphorylated Pol II synthesizes RNA and
    leaves the promoter region behind
  • GTFs are left at the promoter or dissociate from
    Pol II

32
Elongation and Termination
  • Elongation is controlled by
  • _________ sites, where RNA Pol will hesitate
  • _________, which proceeds past the normal
    termination point
  • _________ _________ _________ _________ (P-TEF)
    and _________ _________ _________ _________
    (N-TEF)
  • Termination
  • begins by stopping RNA Pol the _____________
    consensus sequence for termination is ___________

33
Gene Regulation
  • _________ _________ - regulatory sequences that
    augment or diminish transcription, respectively
  • DNA _________ brings _________ into contact with
    transcription _________ and ____________

34
Eukaryotic Gene Regulation
  • _________ _________ are enhancers that respond to
    certain metabolic factors
  • _________ _________ _________(HSE)
  • _________ _________ _________(GRE)
  • _________ _________ _________(MRE)
  • _________ _________ _________(CRE)
  • Response elements all bind _________(transcription
    factors) that are produced under certain cell
    conditions

35
Response Elements
36
Activation of transcription Via CREB and CBP
  • _________________ CREB does not bind to CREB
    binding protein, and no transcription occurs
  • _________________ of CREB causes binding of CREB
    to CBP
  • Complex with basal complex (RNA polymerase and
    GTFs) activates _________________

37
Structural Motifs in DNA-Binding Proteins
  • Most proteins that activate or inhibit RNA Pol II
    have two _________ _________
  • DNA-binding domain
  • transcription-activation domain
  • DNA-Binding domains have domains that are either
  • _________________________
  • _________________________
  • _________________________

38
Helix-Turn-Helix Motif
  • Hydrogen bonding between amino acids and DNA

39
Zinc Finger Motif
  • Motif contains 2 cysteines and 2 His --12 amino
    acids later
  • Zn binds to the repeats

40
Basic Region Leucine Zipper Motif
  • Many transcription factors contain this motif,
    such as CREB (Biochemical Connections, page 315)
  • Half of the protein composed of basic region of
    conserved Lys, Arg, and His
  • Half contains series of Leu
  • Leu line up on one side, forming hydrophobic
    pocket

41
Helical Wheel Structure of Leucine Zipper
42
Transcription Activation Domains
  • _________________________ domains - rich in Asp
    and Glu. Gal4 has domain of 49 amino acids, 11
    are acidic
  • _________________________ domains - Seen in
    several transcription factors. Sp1 has 2
    glutamine-rich domains, one with 39 Glu in 143
    amino acids
  • _________________________ domains - Seen in CTF-1
    (an activator). It has 84 amino acid domain, of
    which 19 are Pro

43
Post Transcriptional RNA Modification
  • ____________________________________ are all
    modified after transcription to give the
    functional form
  • the initial size of the RNA transcript is greater
    than the final size because of the leader
    sequences at the 5 end and the trailer sequences
    at the 3 end
  • the types of processing in prokaryotes can differ
    greatly from that in eukaryotes, especially for
    _______________
  • Modifications
  • ____________________ of leader and trailer
    sequences
  • addition of _____________ _________ (after
    transcription)
  • modification of the structure of specific bases
    (particularly in _______________)

44
Posttranscriptional Modification of tRNA Precursor
45
Modification of tRNA
  • tRNA- the precursor of several tRNAs is can be
    transcribed as ________ polynucleotide sequence
  • _________________________________________________
    ___________ all take place
  • ____________________ ________________ of
    ____________________ are the two most usual types
    of base modification

46
Modification of rRNA
  • Ribosomal RNA
  • processing of rRNA is primarily a matter of
    ________________________________________
  • in _______________, 3 rRNAs in one intact
    ribosome
  • in _______________, ribosomes have 80s, 60s, and
    40s subunits
  • base modification in both prokaryotes and
    eukaryotes is primarily by _____________________

47
Modification of mRNA
  • Includes the capping of the 5 end with an
    N-methylated guanine that is bonded to the next
    residue by a 5?5 triphosphate.
  • Also, 2-O-methylation of terminal ribose(s)

48
mRNA Modification
  • A polyadenylate tail that is usually100-200
    nucleotides long, is added to the 3 end before
    the mRNA leaves the nucleus
  • This tail protects the mRNA from nucleases and
    phosphatases
  • Eukaryote genes frequently contain intervening
    base sequences that do not appear in the final
    mRNA of that gene product
  • Expressed DNA sequences are called exons
  • Intervening DNA sequences that are not expressed
    are called introns
  • These genes are often referred to as split genes

49
Organization of Split Genes in Eukaryotes
50
The Splicing Reaction
  • Exons are separated by intervening
    _______________
  • When the exons are spliced together, a
    _______________ forms in the intron

51
Ribozymes
  • The first ribozymes discovered included those
    that catalyze ______________________________
  • More recently, ribozymes have been discovered
    that are involved in _______________
    _______________
  • _______________ribozymes
  • require an external guanosine
  • example pre-rRNA of the protozoan Tetrahymena
    (next screen)
  • _______________ribozymes
  • display a ______ mechanism similar to mRNA
    splicing
  • no requirement for an external nucleotide

52
Self-splicing of pre-rRNA
Write a Comment
User Comments (0)
About PowerShow.com