Protein Synthesis Mrs. Gamari

Flow of Genetic Information Gene  segment of DNA that codes for a hereditary character (PROTEIN) DNA  RNA  protein PROTEINS ARE IMPORTANT!

Ribonucleic Acid (RNA) Ribose sugar Nitrogenous Bases ADENINE GUANINE CYTOSINE URACIL Single-stranded Shorter in length (length of only one gene)

Types of RNA Each of the three major types of RNA play a different role in protein synthesis and has a different structure

Messenger RNA mRNA Carries instructions from a gene (DNA) in the nucleus to the ribosomes in the cytoplasm.

Transfer RNA tRNA Brings amino acids to the ribosome to help build the protein

Ribosomal RNA rRNA Part of structure of ribosome. RIBOSOME  place where protein synthesis takes place

Transcription Process by which the genetic instructions in a specific gene are rewritten into an RNA molecule. DNA  RNA TAKES PLACE IN NUCLEUS

Steps Enzyme unwinds DNA molecule by breaking hydrogen bonds. Enzyme (RNA Polymerase) adds free RNA nucleotides that are complementary to nucleotides on DNA template strand. DNA strand not used is called the non-template strand Enzyme reaches “termination signal” at end of gene. RNA and DNA molecule separate. mRNA needs to be processed before leaving the nucleus. TRANSCRIPTION ANIMATIONTranscription Animation 2

Why is the mRNA code shorter than the DNA code? Answer: code on the DNA is interrupted periodically by sequences that are not in the final mRNA.

How is mRNA processed? Introns- sequences that interrupt the DNA code- are cut out of the pre-mRNA. Sequences that remain are called exons and they code for proteins. A protective cap (5’ end) and poly-A tail (3’ end) are added to the mRNA molecule

END RESULT RNA can leave the nucleus and perform its job in the cell. Could be mRNA, tRNA, or rRNA (all involved in protein synthesis at some point). Practice Strand (DNA): AGCGCATACGAC mRNA?

The Genetic Code Universal to all life on Earth and supports the idea that organisms share a common ancestor Letters of the code = three adjacent nucleotides (CODON) Word= amino acid Sentence= protein

Translation RNA  Protein Scientists discovered that the real “code” is each group of three bases within mRNA called a codon.  mRNA: AUG CGA CUG CCA GUC CCU AGC

Translation  the making of a protein Protein Structure Amino acids  the building blocks of a protein. Polypeptide  chains of amino acids linked by peptide bonds. Sequence is specific to protein. oteins/labManual/chapter_2.htm

The Code 20 different amino acids can be used to build proteins… 61 codons code for certain amino acids AUG = start codon- signals where ribosome should begin reading the mRNA UAA, UAG, and UGA = do not code for amino acids… “stop codons” that stop the transcription/translation process

mRNA codon chart

Steps of Translation mRNA travels to the ribosome. The ribosome starts reading the mRNA strand 3 bases (CODON) at a time.

A tRNA molecule carries the amino acid methionine (start codon) at one end and the anticodon UAC at the other end. The anticodon helps the tRNA molecule locate where the amino acid should be placed in the growing protein.

Another tRNA molecule with correct anticodon for second codon comes in with another amino acid. The first tRNA molecule leaves and methionine (amino acid) bonds to the second amino acid.

mRNA moves along ribosome, tRNA molecules with correct anticodon keep bringing their amino acids and protein keeps growing

Ribosome reaches stop signal/codon. Polypeptide falls off. tRNA leaves, ribosome and mRNA separate. Transcription/translation of a gene in DNA is complete- a protein is made. Translation Animation Translation Animation 2

Steps for Solving Problems Determine the mRNA molecule built from a DNA template (if not already done). Divide the mRNA molecule into groups of 3 bases (codons). Use the codon chart to determine the order for amino acids. Stop “translating” when you get to a stop codon.

You try it! Use the mRNA chart to determine the sequence of amino acids for each mRNA codon.  mRNA  AUG CAA UGU GAA UAA  Amino acids  Translation Animation

Mutations A permanent change in the DNA of a cell Missense mutation: change in DNA results in wrong amino acid placed in protein. (Might still be ok….) Nonsense mutation: change in DNA causes translation to stop early. (VERY BAD)

Point mutation  base substitution (C instead of G) EXAMPLE: CCU mutates to CCC CCU mutates to CAU Addition/Deletion  “Frame shifts”… cause change in the codon groupings and several amino acids down the line. EXAMPLE: CAGGCUAGC CAGCGCUAGC

General Bio Transcription and Translation

Transcription Takes place in the nucleus of the cell The instructions of DNA are converted into a message of RNA in order to go and build proteins at the ribosome.

Base-pairing Rules for Building mRNA Adenine pairs with Uracil Guanine pairs with Cytosine EXAMPLE  DNA  A C G T G C A  mRNA  U G C A C G U

You try it! DNA  G T T A C A C T T A A C G A C mRNA  After the mRNA molecule is built, it leaves the nucleus to travel to the ribosome. TRANSCRIPTION ANIMATION

Translation – building of protein Takes place at the ribosome in the cell. The instructions carried by mRNA are used to build proteins. The ribosome reads the mRNA three bases at a time, otherwise known as a codon.

You try it! Break the RNA code below into codons.  mRNA  C A A U G U G A A U U G C U G

Here come the amino acids! Transfer RNA (tRNA) brings amino acids to the ribosome according to the codons of the mRNA. Several amino acids connected make up a protein.

mRNA codon chart

You try it! Use the mRNA chart to determine the sequence of amino acids for each mRNA codon.  mRNA  CAA UGU GAA UUG CUG  Amino acids  Translation Animation

Mutations Mutations affect the cell by possibly changing the sequence of amino acids and thus the protein being coded for.  EXAMPLE: CCU = proline  Mutation: CAU= histidine