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RNA andTranscription
Lecture #24Honors Biology
Ms. Day
Gene expression DNA contains…
information in a specific sequence (order) of nucleotides along 2 DNA strands
Leads to specific traits Gene expression includes two stages
Transcription: DNA RNA “transcribe” = to copy into another form
Translation: RNA polypeptide “translate” = to change into another
language
THINK: Translation
happens “LATER”
What are the characteristics of RNA?
Ribose Nucleic Acid Single stranded Made of sugars (called ribose), phosphate groups
and nitrogen bases Backbone= alternating ribose sugar/phosphates
held together by PHOSPHODIESTER BONDS Made of RNA nucleotides Contains bases:
(A) Adenine (G)Guanine (C) Cytosine (U) Uracil (replaces Thymine)
Type of RNA Function Job Picture
mRNA (messenger RNA)
Brings message from DNA (DNA instructions) to
ribosome to make protein
tRNA (transfer RNA)
Transfers/moves amino acids to
ribosomes
rRNA (ribosomal RNA)
Makes up ribosomes along
with proteins
The Ribosome
Part of cell where translation (protein synthesis) occurs
Where proteins are actually made
Basic Principles of Transcription and
TranslationTranscription (uses mRNA)
the synthesis of RNA from DNA Produces messenger RNA (mRNA) Occurs in the nucleus of eukaryotes and
nucleid region of prokaryotesTranslation (uses mRNA, tRNA, rRNA)
actual synthesis of a polypeptide mRNA polypeptide protein Occurs on ribosomes
In prokaryotes, transcription and translation occur together
Prokaryotic cell. In a cell lacking a nucleus, mRNAproduced by transcription is immediately translatedwithout additional processing.
TRANSLATION
TRANSCRIPTIONDNA
mRNA
Ribosome
Polypeptide
In eukaryotes, pre mRNA transcripts are modified (changed) before becoming true “mature” mRNA
Eukaryotic cell. The nucleus provides a Separate compartment for transcription. The original RNA transcript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA.
(b)
TRANSCRIPTION
RNA PROCESSING
TRANSLATION
mRNA
DNADNA
Pre-mRNA
Polypeptide
Ribosome
Nuclearenvelope
“Transcript” is a fancy word for
“message”
How is Protein Made?
Cells are controlled by a cellular chain of commandDNA RNA protein
Called the “Central dogma of biology”
What are proteins made out of? Amino acids
There are 20 different amino acids building blocks of proteins
All living things use the same 20 amino acids to make proteins!!!
The Genetic Code
It’s a table used that TRANSLATES RNA nucleotides (or mRNA “words”) into one of the 20 amino acids3 letter mRNA “word” = 1 amino acid
There are 4 different RNA “letters” that can be used to make “words” A, U, C, and G
Codons: Triplets of Bases
nonoverlapping base triplet is a codon 3 letter mRNA “words” = codon
FOUND ONLY ON mRNA Codons must be read in the correct
order For specified polypeptide to be
producedAlways read in the 5’ 3’ direction
THE GENETIC
CODE
64 CODONS TOTAL
During transcription, a gene determines the sequence of bases along length of mRNA.
Figure 17.4
DNAmolecule
Gene 1
Gene 2
Gene 3
DNA strand(template)
TRANSCRIPTION
mRNA
Protein
TRANSLATION
Amino acid
A C C A A A C C G A G T
U G G U U U G G C U C A
Trp Phe Gly Ser
Codon
3 5
35
TranscriptionDNA RNA mRNA is made by RNA polymerase
breaks DNA strands apart (breaks H bonds btw bases) and hooks together RNA nucleotides
TranscriptionFollows same DNA base-pairing rules, except in RNA, uracil
substitutes for thymine A = U (T on DNA = A in RNA)
C = G
Synthesis of an RNA Transcript
Initiation DNA strands unwind RNA polymerase binds DNA at a special place called a
promoter “TATA box” = start signal on DNA promoter
Determines which strand is used as template only 1 side is used at a time!
Elongation RNA polymerase makes mRNA by reading DNA’s
message Termination
mRNA transcript is released at terminator signal RNA polymerase detaches from the DNA
Transcription Animation
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf
http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html
Another good animation http://www.biostudio.com/d_
%20Transcription.htm
Pre-mRNA Modification:pre-mRNA mature mRNA
Eukaryotic cells modify (process) mRNA after transcription First mRNA made is called pre-mRNA
Pre-mRNA made into mRNA2 things have to happen…
NOT IN PROKARYOTES
1. Alteration of mRNA Ends
Each end of a pre-mRNA is capped 5 end gets a GTP cap 3 end gets a poly-A tail
Figure 17.9
GTPadded to the 5 end
LOTS of adenine nucleotidesadded to the 3 end
Protein-coding segment
Poly-A tailStop codonStart codon5 Cap
AAA…AAA
TRANSCRIPTION
RNA PROCESSING
DNA
Pre-mRNA
mRNA
TRANSLATION
Ribosome
Polypeptide
G P P P
5
The function of the 5’ cap is: prevents mRNA degradation helps attach to the ribosome
Function of the 3’ tail (Poly A cap): prevents mRNA degradation Exports mRNA from nucleus into cytoplasm
2. RNA Splicing
RNA splicingRemoves introns and joins exons
Introns = non-coding regions Exons = coding regions that EXIT nucleus
Figure 17.10
TRANSCRIPTION
RNA PROCESSING
DNA
Pre-mRNA
mRNA
TRANSLATION
Ribosome
Polypeptide
5 Cap
Exon
Intron5 3Poly-A tail
Poly-A tail
Introns cut out andIntrons cut out andexons spliced togetherexons spliced together
Codingsegment
5 Cap
Exon Exon
Intron
Mature mRNA
Pre-mRNA
RNA Animations #1
www.geneticsplace.com
CHAPTER 14: RNA Animations
RNA BiosynthesismRNA Production in Eukaryotes
RNA Splicing
RNA Splicing Animations #2
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html#
http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/interactivemedia/activities/load.html?19&B