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