TRANSCRIPTION & TRANSLATION: From DNA to Protein Chapter 11, Section 2

Genes & Proteins geneWhat is the function of a gene? –Codes for traits, inherited from parents Hair color, attached earlobes, widow’s peak –Provide recipe for making specific proteins Proteins make up muscles, hair, tissues, enzymes, & pigments Protein Synthesis = reading the DNA, forming RNA, using RNA to make the protein (DNA  RNA  Protein)

RNA = Ribonucleic acid RNA is a nucleic acid (like DNA) Key differences between DNA and RNA: DNARNA Number of Strands 21 Nucleotide Sugar DeoxyriboseRibose Nitrogenous Base Pairs Thymine(T), Adenine(A), Guanine (G), Cytosine (C) Uracil (U), Adenine(A), Guanine (G), Cytosine (C)

3 Main Types of RNA 3 Main Types of RNA Copy the table below! Type of RNAStructureLocationFunction mRNA Messenger RNA rRNA Ribosomal RNA tRNA Transfer RNA

3 Main Types of RNA 1. Messenger RNA (mRNA) Structure: single strand, usually straight line Location: moves from nucleus through nuclear pore into cytoplasm to ribosomes

mRNA continued Function: Carries “message” contained on DNA to the ribosomes in the cytosol –Single strand can fit through nuclear pores, unlike double stranded DNA Message is then used to create proteins that will express the trait

2.Ribosomal RNA (rRNA) Structure –Part of the structure of ribosomes –2 part snowman turned upside down Location –In ribosomes: In cytosol and rough endoplasmic reticulim –Created in nucleolus Function –Codes for creation of ribosomes

3. Transfer RNA (tRNA) Structure: Clover-leaf like, looks like a “t” Location: In cytosol Function: –Carries amino acids to ribosome to create a polypeptide chain of amino acids –Has an anticodon that matches up with codon on mRNA

How do we take the genetic code and actually make something from it? Well, first we have to get the code “heard” Then we have to convert it to a language that is understood Processes of: –Transcription –Translation

Transcription Transcription = enzymes make RNA by copying a portion of DNA in the nucleus –Remember, DNA is too big to leave the nucleus! If a DNA sequence is AATCCGGA, what is the complimentary RNA sequence? (Remember RNA doesn’t have Thymine, it has Uracil instead) AATCCGGA (DNA) UUAGGCCU (RNA) The mRNA that gets sequenced is sent out of the nucleus to help make protein

Note Quiz 3/8/12 Take a small sheet of paper, put your name, the date, and class per. 1.What are 2 differences between the structure of RNA and DNA? 2.Which comes first: translation or transcription? 3.Which type or RNA transports the message from the DNA inside the nucleus to the ribosomes in the cytoplasm. You have 3 minutes. Turn it in when you are done.

Genetic Code A certain sequence of Nitrogenous Bases codes for a specific Amino Acid needed to make a Protein Codon = the nitrogenous bases of 3 adjacent nucleotides in mRNA that code for –Start Signal (starts the protein making process) –Stop Signal (stops the protein making process) –Amino Acid An amino acid can be coded for by more than one codon 20 amino acids combine in different combinations to make various proteins

Transcription and Translation How DNA codes for proteins

Rerview: Transcription – Step I A C G T A T C G C G T AT G C A T A G C G C A T DNA Strands

Transcription – Step II A C G T A T C G C G T A U G C A U A G C G C A U One side of the DNA is Matched Up with a Complementary mRNA strand

Transcription Reminders The template strand is the DNA strand being copied The mRNA strand is the same as the DNA strand except Us have replaced Ts

Template DNA Complimentary mRNA strand Codons on mRNA TACGAGTTA AUGCUCAAU Anti-codons on tRNA UACGAGUUA  What is the purpose of the anti-codons? Overview: DNA  RNA  Protein

Translation Translation = using the mRNA to make protein, reading the codons Location: at the ribosomes which attach to the mRNA tRNA is the carrier that comes in bringing the amino acid coded for by the mRNA codons tRNA has an anticodon that pairs up with the mRNA codon mRNA codon: UUG tRNA anti-codon: AAC

Translation cont’d: As tRNAs and their amino acids meet at the ribosomes, the amino acids become linked –Bond together by formation of peptide bonds –Form a linear chain This chain of amino acids folds up on itself and creates a 3-dimensional protein –Proteins are just a chain of amino acids that have folded into a specific shape

 mccd.edu/biol/ap 1int.htm#dna mccd.edu/biol/ap 1int.htm#dna mccd.edu/biol/ap 1int.htm#dna

3 Steps of Protein Synthesis 1.Start: Ribosome binds to mRNA at start codon (AUG) 2.Elongation: –tRNA binds anti-codon to mRNA codon –The ribosome moves from codon to codon along the mRNA. –Amino acids are added one by one 3.Release: release factor binds to the stop codon

Remember: tRNA structure 3-base code (triplet) is an “anticodon” on one end Attached amino acid that is carried from cytoplasm to ribosomes on the other AminoAcid