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

Protein Synthesis Animation

What is the relationship between chromosomes, DNA and 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.

What does every gene “code” for? Proteins

What are the monomers that build proteins? Amino Acids

Where is the DNA kept inside a cell? Inside the nucleus

Which organelle is the site of protein synthesis? Ribosomes

DNA How do we get from here, to there?

DNA Trait Ribosome RNA GENE Protein

REVIEW: Structure of RNA  All forms of RNA have:  Single stranded chain of nucleotides  RNA nucleotides composed of: 1. Phosphate 2. Ribose sugar 3. Nitrogenous base  4 Nitrogen bases of RNA: 1. Guanine 2. Cytosine 3. Adenine 4. Uracil

DNARNA StructureDouble Stranded Single Stranded Bases- PurinesAdenine (A) Guanine (G) Adenine (A) Guanine (G) Bases - Pyrimidines Cytosine (C) Thymine (T) Cytosine (C) Uracil (U) SugarDeoxyriboseRibose Differences between DNA and RNA: 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

What is the purpose of the genetic code in DNA?

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

Stop here and practice!!

Bell Work 1. What is the ultimate purpose of the genetic code in DNA? 2. How do we “read” that code?

Bell Work  DNA contains the hereditary information for life. Which structure in DNA illustrates where that information is held? A B D C

Observe: how many bonds are between A-T and C-G? 2 3

PROTEIN SYNTHESIS STANDARDS  CLE Investigate how genetic information is encoded in nucleic acids.  CLE Describe the relationships among genes, chromosomes, proteins, and hereditary traits.  Use models of DNA, RNA, and amino acids to explain replication and protein synthesis. OBJECTIVES  Investigate how the genetic code carried on mRNA is translated into a protein  Practice “decoding” genetic codes  Create unique genetic code to encrypt a secret message

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 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 genetic code is read 3 letters at a time.

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

Translation animation Translation animation Translation animation – mcgraw hill

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  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  

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