دور مجتمعات التعلم في تحسين جودة الحياة الجامعية .pdf
The_Transcription.pptx
1. The Principals of Genetic
Lectures
Kafrelsheikh University
Faculty of Agriculture
Genetics Department
Dr. Abdel-Hamid Ali
Prof. Of Cyto-biochemical Genetics &
Plant Biotechnology
5. Transcription and translation in
eukaryotic cells are separated in
space and time.
Extensive processing of primary
RNA transcripts in eukaryotic cells.
6. What is a gene?
“The entire nucleic acid sequence that is
necessary for the synthesis of a functional
polypeptide or RNA molecule”.
لتخليق ضروري النووي الحمض من تتابع عن عبارة
.RNA أوجزئ الببتيد متعددة وظيفية سلسلة
8. II. Transcription: RNA from DNA
What is the enzyme that can direct RNA synthesis?
RNA polymerase - first isolated in liver of rats
- requires NTPs with ribose as sugar
- NO primer is needed
n(NTP) (NMP)n + n (Ppi)
DNA
enzyme
RNA polymerase well characterized in E. coli - 6 subunits
9. Making Sense of the Strands
• DNA coding strand = Sense Strand
• DNA template strand = Antisense Strand
• mRNA formed = Sense Strand
3’
5’ 3’
5’
mRNA 5’ 3’
Coding or Partner strand
Template strand
10. Components of Prokaryotic Transcription
3 main steps of transcription: initiation, elongation, termination
19. subunit MW function
36512
Determine the DNA to be
transcribed
150618 Catalyze polymerization
155613 Bind & open DNA template
70263
Recognize the promoter
for synthesis initiation
RNA-pol of E. Coli
25. Transcription initiation by prokaryotic RNA polymerase
Core enzyme
Holoenzyme
’
Promoter
-35 -10
“sliding and scanning”
Open complex; initiation
’
Closed complex
rNTPs
PPi
’
5’pppA
mRNA
Sigma separates
from the core
once a few
phosphodiester
bonds are formed
31. Elongation
• Polymerase is accurate - only about 1 error in
10,000 bases
• Elongation rate is 20-50 bases per second -
slower in G/C-rich regions (why??) and faster
elsewhere.
35. 19.15 Bacterial RNA Polymerase
Terminates at Discrete Sites
• Intrinsic termination requires
recognition of a terminator
sequence in DNA that codes for
a hairpin structure in the RNA
product.
• The signals for termination lie
mostly within sequences already
transcribed by RNA polymerase,
and thus termination relies on
scrutiny of the template and/or
the RNA product that the
polymerase is transcribing. FIGURE 28: An intrinsic
terminator has two features
50. “The Protein Players” - RNA polymerases, transcription factors, initiation
factors, enhancers, repressors
51. Protein Synthesis: Translation
Translation is the process of decoding a mRNA
molecule into a polypeptide chain or protein.
mRNA جزيء تشفير فك عملية هي الترجمة
إلى
بروتين أو ببتيد سلسلة
.
Each combination of 3 nucleotides on mRNA is called a
codon or three-letter code word.
Each codon specifies a particular amino acid that is to be
placed in the polypeptide chain (protein).
وتسمى
كل
تركيبة
من
3
النيوكليوتيدات
على
mRNA
كودون
أو
ثالثة
أحرف
كلمة
الشفرة
.
يحدد
كل
كودون
حمض
أميني
معين
وهذا
هو
وضعها
في
سلسلة
ببتيد
(
بروتين
)
.
55. 55
The Genetic Code
Marshall Nirenberg identified the codons
that specify each amino acid.
RNA molecules of only 1 nucleotide and of
specific 3-base sequences were used to
determine the amino acid encoded by
each codon.
The amino acids encoded by all 64 possible
codons were determined.
57. 57
The Genetic Code
stop codons: 3 codons (UUA, UGA, UAG)
in the genetic code used to terminate
translation
start codon: the codon (AUG) used to
signify the start of translation
The remainder of the code is degenerate
meaning that some amino acids are
specified by more than one codon.
58. Transfer RNA
• anticodon- 3’ to 5’ sequence that matches
the complementary 5’ to 3’sequence
(codon) on the mRNA
• Acceptor arm - Amino acid code on 3’ end
• T and D loops – provide structure for
interface with aminoacyl-tRNA synthetase
?
64. Ribosomes
2 subunits, separate in cytoplasm
until they join to begin translation
Large
Small
Contain 3 binding sites
E (exit).
P (peptidyl)
A (aminoacyl)