Chapter 5 RNA and Transcription From Gene to Protein Honors Genetics Ms. Day

Introduction to RNA and Gene Expression What is RNA? https://www.youtube.com/watch?v=0Elo-zX1k8M What is Gene Expression? https://www.youtube.com/watch?v=gG7uCskUOrA

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)

Brings message from DNA (DNA instructions) to ribosome to make protein 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 Translation Transcription (uses mRNA) DNA RNA Produces messenger RNA (mRNA) Occurs in the nucleus of eukaryotes and nucleoid region of prokaryotes Translation (uses mRNA, tRNA, rRNA) mRNA  polypeptide  protein (leads to trait) Occurs on ribosomes

In prokaryotes, transcription and translation occur together Prokaryotic cell. In a cell lacking a nucleus, mRNA produced by transcription is immediately translated without additional processing. TRANSLATION TRANSCRIPTION DNA mRNA Ribosome Polypeptide

“Transcript” is a fancy word for “message” 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 DNA Pre-mRNA Polypeptide Ribosome Nuclear envelope “Transcript” is a fancy word for “message”

How is Protein Made? Cells are controlled by a cellular chain of command DNA 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 A table used that TRANSLATES RNA nucleotides (or mRNA “letters”) into one of the 20 amino acids 3 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 RNA codes information as a sequence of nonoverlapping base triplets, or codons 3 letter mRNA “words” = codon FOUND ONLY ON mRNA Codons must be read in correct order For specified polypeptide to be produced Always read in the 5’  3’ direction

THE GENETIC CODE

Evolution of the Genetic Code The genetic code is nearly universal Shared by organisms from the simplest bacteria to the most complex animals All 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 DNA molecule Gene 1 Gene 2 Gene 3 DNA strand (template) TRANSCRIPTION mRNA Protein TRANSLATION Amino acid A C G T U Trp Phe Gly Ser Codon 3 5

Only 1 enzyme used called RNA polymerase Transcription DNA  RNA Only 1 enzyme used called RNA polymerase Opens DNA helix (breaks H bonds btw bases) Hooks together RNA nucleotides

Transcription Follows 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://highered.mheducation.com/sites/0072507470/student_view0/chapter3/animation__mrna_synthesis__transcription___quiz_1_.html Another good animation https://www.dnalc.org/resources/3d/12-transcription-basic.html

Termination of Transcription Different in prokaryotes and eukaryotes Prokaryotes 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 Eukaryotes RNA 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 mRNA 2 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 A modified guanine nucleotide added to the 5 end 50 to 250 adenine nucleotides added to the 3 end Protein-coding segment Polyadenylation signal Poly-A tail 3 UTR Stop codon Start codon 5 Cap 5 UTR AAUAAA AAA…AAA TRANSCRIPTION RNA PROCESSING DNA Pre-mRNA mRNA TRANSLATION Ribosome Polypeptide G P 5 3 Figure 17.9

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 Modification Removes introns and joins exons Introns = non-coding regions Exons = coding regions that EXIT nucleus TRANSCRIPTION RNA PROCESSING DNA Pre-mRNA mRNA TRANSLATION Ribosome Polypeptide 5 Cap Exon Intron 5 3 Poly-A tail Introns cut out and exons spliced together Coding segment 1 146 3 UTR 5 UTR Intron Pre-mRNA Exon Exon Mature mRNA Figure 17.10

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# Interactive tutorial http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/interactivemedia/activities/load.html?19&B

Heterochromatin vs Euchromatin…please add to PPT guide! does NOT contain actively transcribed DNA Euchromatin DOES contain actively transcribed DNA “Eu” (you) need these genes for traits