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

Objectives over next few lessons: Can differentiate between DNA and RNA Can explain steps of Transcription Can explain steps of Translation Can summarize how to get from DNA code to the expression of a trait Can summarize the relationship between chromosomes, genes and DNA

Face Partners

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 is the purpose of the genetic code in DNA? To create proteins

Objective: Be able to explain how we get from DNA code to expression of a trait Gene Trait Protein

Bacon – explain the purpose of the DNA code

Central Dogma The basic idea of how hereditary information flows from DNA sequence to create functioning proteins

Two Types of Nucleic Acids DNA – Deoxyribonucleic acid RNA – Ribonucleic acid Need both types of nucleic acids to get from the DNA code to producing proteins

RNA DNA Single Stranded & short (one gene) Double Stranded & long (1000s genes) Base Pairs: A-T C-G Base Pairs: A-U C-G Sugar: Ribose Sugar: Deoxyribose

RNA’s JOB = Use DNA code to make proteins!! Differences between DNA and RNA: DNA 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 = Use DNA code to make proteins!!

Eggs – tell bacon how to differentiate between DNA and RNA

Types of RNA mRNA – Messenger RNA rRNA – Ribosomal RNA tRNA – Transfer RNA Short single strand that carries a copy of the DNA code for one gene from the nucleus to the ribosome Combines with proteins to make the ribosome. Carries amino acids to the ribosome to build a protein chain.

What does every gene “code” for? Proteins

What are the monomers that build proteins? Amino Acids

DNA Structure To crack the genetic code found in DNA we need to look at the sequence of bases. The sequence of bases are read in triplets (sets of 3) called codons. A G G - C T C - A A G - T C C - T A G T C C - G A G - T T C - A G G - A T C Each codon codes for a specific amino acid

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

Which organelle is the site of protein synthesis? Ribosomes

DNA cannot leave the nucleus, so…

DNA GENE RNA Ribosome Protein Trait

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

Protein Synthesis Animation

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

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

Making mRNA RNA polymerase : enzyme that unravels a segment of DNA (gene) and builds a complementary mRNA strand based off DNA template Example: DNA strand: A T G G G A A C T T A C mRNA strand: U A C C C U U G A A T G After mRNA strand is complete – DNA reforms and mRNA leaves the nucleus and heads to ribosomes

mRNA synthesis animation

Bacon – summarize the process of transcription for eggs

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

Eggs – explain how to tell the difference between replication and transcription

Stop here and practice!!

Bell Work What is the ultimate purpose of the genetic code in DNA? 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? B A C D

PROTEIN SYNTHESIS STANDARDS OBJECTIVES CLE 3210.4.1 Investigate how genetic information is encoded in nucleic acids. CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits. 3210.4.1 - Use models of DNA, RNA, and amino acids to explain replication and protein synthesis. 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 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.

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 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.

Your Task Draw a flow chart to show how to get from: