RNA and Transcription Lecture #24 Honors 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 RNAFunction JobPicture 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) the synthesis of RNA from DNA Produces messenger RNA (mRNA) Occurs in the nucleus of eukaryotes and nucleid region of prokaryotes Translation (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, mRNA produced by transcription is immediately translated without additional processing. TRANSLATION TRANSCRIPTION DNA 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 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 It’s a table used that TRANSLATES RNA nucleotides (or mRNA “words”) into one of the 20 amino acids 3 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 produced Always 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 DNA molecule Gene 1 Gene 2 Gene 3 DNA strand (template) TRANSCRIPTION mRNA Protein TRANSLATION Amino acid ACC AAACCGAG T UGG U UU GGCUC A Trp Phe Gly Ser Codon

Transcription DNA  RNA mRNA is made by RNA polymerase breaks DNA strands apart (breaks H bonds btw bases) and 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 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 mat/molgenetics/transcription.swf mat/molgenetics/transcription.swf class.unl.edu/biochem/gp2/m_biology/animati on/gene/gene_a2.html class.unl.edu/biochem/gp2/m_biology/animati on/gene/gene_a2.html Another good animation

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 is capped 5 end gets a GTP cap 3 end gets a poly-A tail Figure 17.9 GTP added to the 5 end LOTS of adenine nucleotides added to the 3 end Protein-coding segment Poly-A tail Stop codon Start codon 5 Cap AAA…AAA TRANSCRIPTION RNA PROCESSING DNA Pre-mRNA mRNA TRANSLATION Ribosome Polypeptide G PPP 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 splicing Removes introns and joins exons Introns = non-coding regions Exons = coding regions that EXIT nucleus Figure 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 5 Cap Exon Intron Mature mRNA Pre-mRNA

RNA Animations #1 CHAPTER 14: RNA Animations RNA Biosynthesism RNA Production in Eukaryotes RNA Splicing

RNA Splicing Animations #2 hill.com/sites/ /student_view0/cha pter15/animations.html hill.com/sites/ /student_view0/cha pter15/animations.html hill.com/sites/ /student_view0/cha pter15/animations.html# hill.com/sites/ /student_view0/cha pter15/animations.html# l_biology_7/media/interactivemedia/activities/l oad.html?19&B l_biology_7/media/interactivemedia/activities/l oad.html?19&B