Protein Synthesis: Transcription & Translation Chapter 12-3 DNA > mRNA > ribosome > protein 1

Learning Goals 1. Summarize the overall process of protein synthesis including the “central dogma”. 2. Describe Transcription in detail including where it takes places and the roles of introns and exons. 3. Describe Translation in detail including where it takes place, codons, anti-codons, tRNA, amino acids, and protein 4. Explain how gene expression works.

DNA > RNA > ribosome > protein Protein Synthesis Central Dogma Rule: DNA > RNA > ribosome > protein 3

Protein Synthesis Overview Two processes are required: 1. Transcription: DNA > mRNA 2. Translation: mRNA > protein 4

Transcription: DNA > mRNA Process of making messenger RNA (mRNA) from a DNA template to take the DNA info outside of the nucleus 5

DNA can NOT leave the nucleus (too big) Messenger RNA (mRNA) carries the info encoded in DNA out of the nucleus to the ribosomes located in the cytoplasm. 6

Steps of Transcription 1. DNA strands unwind & separate 2. DNA strand containing a specific gene serves as a template strand 3. RNA nucleotides are matched to complimentary DNA bases 4. mRNA molecule is complete and DNA rewinds

mRNA Processing Introns: the mRNA contains extra info (junk) that must be removed (cut out) Exons: the remaining pieces carry useful information are spliced (connected) together to make the complete mRNA 8

The bases of mRNA pair with DNA bases but RNA replaces T with U DNA: C T G T A C G G A ---> Transcription mRNA: G A C A U G C C U DNA RNA A U T G C template strand 9

Check: Are there any T’s in your mRNA? Now you try… Based on the DNA template, create the matching mRNA strand: DNA: C T A T G C A A A C T A T A G mRNA: ______________________________ G A U A C G U U U G A U A U C Check: Are there any T’s in your mRNA? There shouldn’t be!!!

Translation: mRNA > protein Process of making proteins from info on mRNA mRNA travels out of nucleus to the ribosome, which “reads” the mRNA as a series of 3 letter words called codons 12

Codon: 3-base code on mRNA that codes for a specific amino acid Ex. CGU = alanine GUU = valine The sequence of bases in DNA tell mRNA what order amino acids must join together to make a particular protein. 13

Codons found in mRNA Second Base First Base Third Base 14

Transfer RNA (tRNA) matches up with each codon and transfers the correct amino acid Each tRNA molecule has 3 unpaired bases called the anticodon that is complementary to one mRNA codon. 15

Each amino acid is added to a growing chain of amino acids Protein = peptide bonds connecting amino acids Many different types of proteins exist because the number and sequence of amino acids can be different

Codons found in mRNA Practice translating mRNA into amino acids: First Base Second Base Third Base Codons found in mRNA Practice translating mRNA into amino acids: mRNA: AUG AAA AGU UGU CUG GUU UAA A.A: ______________________________________ Met - Lys – Ser - Cys – Leu – Val - Stop 17

How DNA determines proteins DNA molecules serve as templates for making messenger RNA molecules Messenger RNA molecules move to ribosomes Transfer RNA molecules bring amino acids to the ribosome Polypeptides (proteins) are formed as ribosomes move along the messenger RNA strand

Gene Expression DNA in all of your body cells is the same! Ex: DNA in your eye cells is the same DNA that is in your skin cells. Different types of cells express different genes. Ex: Your eyes may be green, while your skin is brown. Specialization of cells is due to different patterns of gene expression, rather than different genes themselves. Liver cells express different genes than blood cells 19

----Transcription----> mRNA: AUG AGG UCG CGU UGA DNA: TAC TCC AGC GCA ACT ----Transcription----> mRNA: AUG AGG UCG CGU UGA ----Translation---> A.A.: met arg ser arg stop 20

Learning Goals 1. Summarize the overall process of protein synthesis including the “central dogma rule”. 2. Describe Transcription in detail including where it takes places and the roles of introns and exons. 3. Describe Translation in detail including where it takes place, codons, anti-codons, tRNA, amino acids, and protein 4. Explain how gene expression works.