DNA, RNA, Protein Synthesis

DNA Goals The Human Genome List the contributions of various scientists to the idea that DNA carries the genetic code. Describe the structure and function of DNA. Summarize the process of DNA replication.

DNA History The genetic code: the way in which cells store the program that they seem to pass from one generation of an organism to the next generation. Who discovered the molecule that carries the genetic code? How did they do it?

DNA History Frederick Griffith

DNA History Frederick Griffith – experimented with mice and a disease-causing strain of bacteria in which mice got pneumonia and died. Found that one strain of bacteria had been transformed into another He called it Transformation

DNA History Oswald Avery – wanted to test this experiment to see which molecules of the cell were the transforming factors. Found that DNA is the transforming factor DNA is the nucleic acid that stores and transmits the genetic information from one generation of an organism to the next.

DNA History Alfred Hershey and Martha Chase –

DNA History Alfred Hershey and Martha Chase – experimented to find the kinds of viruses that infect bacteria. Known as bacteriophages (composed of a DNA core and a protein coat, they attach themselves to the surface of a bacterium and then inject a material into the bacterium which allows them to replicate themselves)

DNA History Alfred Hershey and Martha Chase – Discovered that only the DNA entered the bacterium and that the protein coat remained outside the bacterium Convincing evidence that DNA contains the genetic information.

DNA STRUCTURE Chromatin is the long uncoiled strand of DNA that makes up chromosomes Chromosomes are coiled DNA

DNA STRUCTURE DNA is coiled around 2 structures: –Histones class of proteins that bind to DNA form tiny particles called nucleosomes –Nucleosomes structure that helps to fold and package DNA plays a role in regulating the way genes are transcribed.

DNA STRUCTURE DNA is a polymer formed from units called Nucleotides Made of 3 basic parts: –A 5-carbon sugar called deoxyribose –A phosphate group –Nitrogenous base

DNA STRUCTURE Nitrogenous bases have two classes: –Purines (larger of the two) Adenine (A) Guanine (G) –Pyrimidines Cytosine (C) Thymine (T)

DNA STRUCTURE Individual nucleotides are joined together to form a long chain. Sugars and phosphate groups form the backbone and the nitrogenous bases stick out to form the rungs of the ladder.

DNA STRUCTURE

How do we know? Rosalind Franklin: used x-ray crystallography to look at a pattern of DNA. -3-D look. Gave important clues on the structure of DNA.

DNA STRUCTURE Chargaff’s Rule: pyrimidines can only pair with purines and visa versa. A-T, T-A : G-C, C-G This base pairing (hydrogen bonding) is the force that holds the two strands of the double helix together.

DNA STRUCTURE James Watson & Francis Crick: Were trying to figure out the three-dimensional model of DNA when they saw Franklins x-ray. Developed the double helix shape The nitrogenous bases on each of the strands are positioned exactly opposite each other Watson and Crick won the Nobel Prize in 1962

DNA STRUCTURE

DNA Molecule DNA Replication Takes place in the nucleus Each half, each strand, is said to be complementary Before the cell divides, it must duplicate its DNA. –Semi-conservative process The duplicated DNA contains part of the old DNA as well as new DNA. This is known as REPLICATION

DNA Replication 4 steps to DNA Replication –DNA molecule unwinds –Hydrogen bonds break between the nitrogen bases –new nucleotides are inserted that are complementary to the original (parent) strand –End up with 2 identical strands of DNA

DNA REPLICATION It is carried out by enzymes: –DNA Helicases unzip or separate the 2 strands of the double helix hydrogen bonds are broken –DNA Polymerases insert the appropriate nucleotides (bases) “proofread” the bases that have been inserted to ensure that they are paired correctly –DNA Ligases seals breaks in the phosphate-sugar backbone of DNA

DNA Replication

DNA - Unseeable Biology

RNA Goals State the function of the different types of RNA. Compare the structures of RNA and DNA. Describe the process of transcription.

RNA Structure acts a messenger or carrier, that brings the genetic info from the DNA (in the nucleus) to the ribosome carries out the process by which proteins are made from amino acids RNA is a polymer formed from units called Nucleotides

RNA Structure Made of 3 basic parts: A 5-carbon sugar called ribose* A phosphate group Nitrogenous base –Purines (larger of the two) Adenine Guanine –Pyrimidines Cytosine Uracil *(RNA only) Is single stranded* RNA can leave the nucleus* *differences from DNA

RNA Structure RNA molecule is a disposable copy of a segment of DNA There are 3 types of RNA –mRNA – messenger carries protein-building instruction –tRNA – transfer delivers amino acids to ribosomes –rRNA – ribosomal makes ribosomes

RNA Structure

RNA Transcription process by which a molecule of DNA is copied into a complementary strand of RNA * mRNA Why necessary? DNA is only found in the nucleus Ribosomes found in the cytoplasm A carrier is needed to bring the genetic information from the DNA in the nucleus to the ribosomes in the cytoplasm

RNA Transcription Steps of TRANSCRIPTION: 1.) RNA polymerase attaches to a special place on the DNA molecule called the Promoter *(“initiator”) – TATA box.Promoter 2.) RNA polymerase separates the two strands of the double helix a.) breaks the hydrogen bonds between the nitrogen bases 3.) RNA nucleotides come in and pair up to the DNA template 4.) RNA polymerase releases the newly synthesized mRNA molecules when it reaches “stop” a.) mRNA leaves the nucleus to go to the ribosome in the cytoplasm

RNA Transcription

Protein Synthesis Goals Explain the terms codon, anticodon. Describe the 3 stages of translation.

Protein Synthesis Proteins are made by stringing together long chains of amino acids. There are 20 amino acids DNA contains only 4 different nitrogenous bases The genetic code must have a four-letter “alphabet” The smallest size for a code word in DNA is three nucleotides (to make 20 amino acids)

Protein Synthesis Codon: each combination of three nucleotides of the mRNA Each codon specifies a particular amino acid that is to be placed in the polypeptide chain. AUG is called the “initiator” codon UAA, UAG, & UGA are called the “stop” codons; they signify the end of the polypeptide sequence.

Protein Synthesis Translation decoding of a mRNA message into a polypeptide chain (protein) using tRNA, rRNA, and the ribosome. –tRNA: there are three exposed bases on each tRNA molecule, these will base pair with a codon on mRNA These nucleotides on the tRNA are called the anticodon Referred to as the taxi service –attached to each tRNA is the amino acid specified by the codon to which it base pairs –by matching the tRNA anticodon to the mRNA codon, the correct amino acid is put into place.

Protein Synthesis

Ribosome: –site where proteins are made –site where mRNA and tRNA come together for protein formation

Initiation mRNA binds to the ribosome Ribosome moves along the mRNA to find the AUG “start” codon to begin translation

Elongation mRNA passes through the ribosome tRNAs deliver amino acids to the ribosome in the order specified by the mRNA Peptide bonds form between the amino acids as the polypeptide (protein) is growing

Termination a stop codon containing release factors is put into place on the ribosome mRNA and the protein are released the protein can now go to work in the cell new polypeptide chain mRNA

Protein Synthesis

DNA – RNA - Protein Putting it all together DNA: TAC GGA TTC CGA GCC ATT TTC mRNA: AUG CCU AAG GCU CGG UAA AAG Amino Acid Sequence: Methionine-Proline-Lysine-Alanine-Arginine- Stop

Protein Synthesis