Chapter 5RNA and

TranscriptionFrom Gene to Protein

Honors GeneticsMs. Gaynor

The Flow of Genetic Information

DNA information in a specific sequence (order)

of nucleotides along 2 DNA strands Leads to specific traits by controlling the

synthesis of proteins 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 “letters”) into one of the 20 amino acids3 letter mRNA “word” = 1 amino acid

There are 4 different RNA “letters” that can be used

A, U, C, and G

Codons: Triplets of Bases

Genetic information is coded as a sequence of nonoverlapping base triplets, or codons

3 letter mRNA “words” = codonFOUND 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

Evolution of the Genetic Code

The genetic code is nearly universalShared by organisms from the simplest

bacteria to the most complex animalsAll organisms have SAME DNA “letters” and SAME RNA “letters”

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 RNA synthesis is done by RNA polymerase

Forces 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 initiates mRNA synthesis at start

point on templates called promoters RNA polymerase binds to promoter

Elongation RNA polymerase moves downstream, unwinding

DNA & elongating mRNA transcript 5 3 direction In wake of transcription, DNA strands re-form a

double helix. Termination

mRNA transcript is released at terminator signal RNA polymerase detaches from the DNA

RNA Polymerase Binding and Initiation of Transcription

Promoters (on DNA) starts RNA synthesis (BOTH prokaryotes & eukaryotes) RNA polymerase binds here then unwinds DNA RNA Polymerase adds new FREE RNA nucleotides

to DNA template strand in 5’ 3’ direction “TATA box” = start signal on DNA promoter

Determines which strand is used as template only 1 side is used at a time!

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

Termination of Transcription

Different in prokaryotes and eukaryotesProkaryotesProkaryotes

RNA polymerase falls off DNA when it hits “termination signal” transcription ends & transcript is released

In prokaryotes, RNA is directly translated into the polypeptide in

cytoplasm.

Termination of Transcription

EukaryotesEukaryotesRNA polymerase transcribes

until it hits a polyadenylation signal (TTATTT)Makes “AAUAAA” on mRNA

Then it falls off mRNA!!!

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 molecule is modified in a particular way 5 end gets a modified nucleotide cap The 3 end gets a poly-A tail

Figure 17.9

A modified guanine nucleotide

added to the 5 end

50 to 250 adenine nucleotidesadded to the 3 end

Protein-coding segment

Polyadenylation signal

Poly-A tail3 UTR

Stop codonStart codon5 Cap 5 UTR

AAUAAA AAA…AAA

TRANSCRIPTION

RNA PROCESSING

DNA

Pre-mRNA

mRNA

TRANSLATION

Ribosome

Polypeptide

G P P P

5 3

The function of the 5’ cap is: prevent mRNA degredation by hydrolytic

enzymes helps attach to the ribosome

Function of the 3’ tail (Poly A cap): same functions as the 5’cap also helps export of mRNA from nucleus

2. Split Genes and RNA Splicing

RNA splicing and RNA ModificationRemoves 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

1 1463 UTR5 UTR

mRNA

Exon Exon

Intron

MaturemRNA

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