RNA and Transcription Lecture #19 Honors Biology Ms. Day https://www.youtube.com/watch?v=gG7uCskUOrA

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)

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) 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

Transcription & Translation DNA mRNA Ribosome Polypeptide

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 https://www.youtube.com/watch?v=-Ht81lHiJac

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

mRNA is made by RNA polymerase breaks DNA strands apart Transcription DNA  RNA mRNA is made by RNA polymerase breaks DNA strands apart 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 binds DNA Elongation RNA polymerase makes mRNA by reading DNA’s message Termination mRNA transcript (mRNA) is released 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