RNA & Protein Synthesis Ribose RNA Hydrogen bonds Mrs. Stewart Biology I Uracil Adenine

Genes A gene is a section of the DNA sequence that codes for a protein. Each unique gene has a unique sequence of bases. This unique sequence of bases will code for the production of a unique protein. It is these proteins and combination of proteins that determine the phenotypes for our traits.

How do we get from here, to there? DNA How do we get from here, to there? Trait

DNA GENE RNA Protein Trait

REVIEW: Structure of RNA All forms of RNA have: Single stranded chain of nucleotides RNA nucleotides composed of: Phosphate Ribose sugar Nitrogenous base 4 Nitrogen bases of RNA: Guanine Cytosine Adenine Uracil

Differences between DNA and RNA: Structure Double Stranded Single Stranded Bases- Purines Adenine (A) Guanine (G) Bases - Pyrimidines Cytosine (C) Thymine (T) Uracil (U) Sugar Deoxyribose Ribose RNA’s JOB= Make Proteins!!

Types of RNA 1) messenger RNA (mRNA)- carries instructions (the message) from the DNA in the nucleus to the ribosome

Types of RNA 2) ribosomal RNA (rRNA)- combines with proteins to form the ribosome (proteins made here) 3) transfer RNA (tRNA)- transfers each amino acid to the ribosome as it is specified by coded messages in mRNA during the construction of a protein

Protein Synthesis Overview There are two steps to making proteins (protein synthesis): 1) Transcription (occurs in the nucleus) DNA RNA 2) Translation (occurs in the cytoplasm) RNA  protein

Transcription occurs in three main steps:

Initiation: Transcription begins when the enzyme RNA polymerase binds to the DNA at a promoter site. Promoters are signals in the DNA strand (a certain sequence of bases) that indicate to the enzyme where to bind to make RNA.

Elongation: The enzyme separates the DNA strands by breaking the hydrogen bonds, and then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA. RNA polymerase pairs up free floating RNA nucleotides with DNA template and joins the nucleotides together to form the backbone of the new mRNA strand.

Termination When mRNA hits a termination sequence, it separates from the DNA

Transcription vs. Replication The main difference: Transcription results in one single-stranded mRNA molecule. Replication results in two double-stranded DNA molecules. Practice DNA template DNA Complement (replication) mRNA (transcription) ATTCGGAGC TAAGCCTCG UAAGCCUCG

mRNA synthesis animation transcription animation

What is the purpose of the genetic code in DNA?

Transcription Nucleus Adenine (DNA and RNA) Cytosine (DNA and RNA) RNA polymerase Adenine (DNA and RNA) Cytosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) Nucleus

After we transcribe the message so it can leave the nucleus, we then must have a way to “read” the message.

The Genetic Code The “language” of mRNA instructions is called the genetic code. This code is written in a language that has only four “letters” (A,G,C,U) How can a code with just 4 letters carry instructions for 20 different amino acids?

The Genetic Code – what does it code for? Proteins (polypeptides) - long chains of amino acids that are joined together. There are 20 different amino acids. The structure and function of proteins are determined by the order (sequence) of the amino acids

The Genetic Code The genetic code is read 3 letters at a time. A codon consists of three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide (protein). The four bases (letters) of mRNA (A, U, G, and C) are read three letters at a time (and translated) to determine the order in which amino acids are added to a protein.

The Codon Wheel 64 different mRNA codons are possible in the genetic code.

More than one codon can code for the same amino acid Example: GGG, GGU, GGA, GGC = Glycine Some codons give instructions Example: AUG = start Example: UGA, UAA, UAG = Stop

Cracking the Secret Code To decode a codon: start at the middle of the circle and move outward. Ex: CGA = Arginine Ex: GAU = Aspartic Acid

Cracking the Code This picture shows the amino acid to which each of the 64 possible codons corresponds. To decode a codon, start at the middle of the circle and move outward. Ex: CGA Arginine Ex: GAU Aspartic Acid

Translation rRNA and tRNA will decode the message on the mRNA strand to produce a polypeptide chain (protein). Translation takes place on ribosomes, in the cytoplasm or attached to the ER.

http://www.youtube.com/watch?v=5bLEDd-PSTQ

Messenger RNA (mRNA) The mRNA that was transcribed from DNA during transcription, leaves the cell’s nucleus and enters the cytoplasm.

Transfer RNA (tRNA) Transfer RNA (tRNA) molecules in the cytoplasm will bond with a specific amino acid Then, tRNA carries that amino acid to the ribosome Each tRNA molecule has three unpaired bases called an anticodon. These bases are complementary to one codon on the mRNA strand.

tRNA molecule Anticodon

Translation

Initiation Begins when an mRNA in the cytoplasm attaches to the ribosome. AUG = the start codon AUG = methionine

The Polypeptide “Assembly Line” tRNA anticodon will temporarily bind to the complementary codon on the mRNA molecule in the ribosome. (This binding of codon to anticodon ensures the correct amino acid is being added)

Elongation The ribosome has two binding sites, allowing two tRNA molecules to line up, side by side The ribosome forms a peptide bond between the first and second amino acids on those tRNA molecules At the same time, the ribosome breaks the bond that held the first tRNA molecule to its amino acid and releases the tRNA molecule.

The Polypeptide “Assembly Line” The tRNA floats away, allowing the ribosome to move down the mRNA molecule and bind another tRNA. The ribosome continues to move along the mRNA, attaching new tRNA molecules and adding more amino acids to the polypeptide chain.

Termination The process continues until the ribosome reaches one of the three stop codons on the mRNA. Then, the ribosome detaches from the mRNA. The result is a polypeptide (protein chain) that is ready for use in the cell.

Practice TAC GGT CCA AAC ACT AUG/CCA/GGU/UUG/UGA UAC/GGU/CCA/AAC/ACU DNA template mRNA (transcription) tRNA Amino Acid Sequence (translation) TAC GGT CCA AAC ACT AUG/CCA/GGU/UUG/UGA UAC/GGU/CCA/AAC/ACU Met-Pro-Gly-Leu-Stop

Computer Practice for transcription and translation http://learn.genetics.utah.edu/content/begin/dna/transcribe/ http://www.youtube.com/watch?v=Ikq9AcBcohA

All organisms use the same genetic code (A,T,C,G). This provides evidence that all life on Earth evolved from a common origin.