DNA, RNA and Protein

A. The Structure of DNA (Deoxyribonucleic Acid) DNA is double stranded and in the shape of a double helix.

2. The monomers of DNA are called nucleotides: made of a sugar (deoxyribose), a phosphate group and a nitrogen base Phosphate group Nitrogen Base Deoxyribose Sugar

3. There are four types of DNA bases and they pair specifically: Adenine Thymine with Guanine Cytosine with

DNA Looks Like a Ladder The alternating sugar and phosphates form the sides of a ladder and the nitrogen bases form the rungs. The Two sides of the ladder are held together with hydrogen bonds

A T C G G C T A T C G A T A G C C G A T A G C T 4. If the sequence of one strand is known, the other strand is known A T C G G C T A T C G A T A G C C G A T A G C T

DNA Works as a Code Codon- a three nucleotide sequence that codes for a single amino acid With 4 different types of nucleotides in triplet codes, 64 combinations are possible 61 of the codons code for 20 amino acids 3 codons signal a stop- Identifies the end of a protein The genetic code is exact. If a sequence of DNA is known, the resulting amino acid chain (protein) is known

DNA codons Amino Acid Isoleucine ATT, ATC, ATA Leucine CTT, CTC, CTA, CTG, TTA, TTG Valine GTT, GTC, GTA, GTG Phenylalanine   TTT, TTC Methionine ATG Cysteine  TGT, TGC Alanine       GCT, GCC, GCA, GCG Glycine   GGT, GGC, GGA, GGG Proline       CCT, CCC, CCA, CCG Threonine   ACT, ACC, ACA, ACG Serine        TCT, TCC, TCA, TCG, AGT, AGC Tyrosine   TAT, TAC Tryptophan   TGG Glutamine   CAA, CAG Asparagine   AAT, AAC Histidine  CAT, CAC Glutamic acid   GAA, GAG Aspartic acid  GAT, GAC Lysine        AAA, AAG Arginine   CGT, CGC, CGA, CGG, AGA, AGG Stop codons TAA, TAG, TGA

DNA Replication

C. DNA Replication The structure of DNA explains how it replicates DNA “unzips” down the middle b) Free floating nucleotides pair up with both sides of the DNA molecule ATCGA TAGCT ATCGA TAGCT ATCGA TAGCT ATCGA TAGCT Original Exactly Copied DNA Strands

DNA Replication This process produces two exact DNA molecules (Chromosomes) that are the same DNA never leaves the nucleus

If DNA never leaves the nucleus, how can the DNA message get to the site of protein production, the ribosome?

Answer: The DNA message is copied to RNA during the process of Transcription

How do RNA and DNA differ?

D. The Structure of RNA RNA is single stranded The sugar in RNA is Ribose, not deoxyribose as in DNA The DNA nucleotide thymine is replaced by the RNA nucleotide Uracil

E. RNA’s Functions: Two Types, Two Jobs m-RNA (messenger RNA) delivers the copied DNA from the nucleus to the Ribosome- the site of protein synthesis t-RNA (transfer RNA) picks up specific amino acids in the cytoplasm and delivers them to the ribosome

Ribosome

F. Steps in Protein Synthesis DNA molecule unzip where the desired gene is located Free floating RNA nucleotides pair with the DNA strand forming m-RNA (Transcription) The m-RNA leaves the nucleus and goes to a ribosome A specific t-RNA delivers a specific amino acid to the ribosome (Translation) The m-RNA codon matches with the t-RNA anticodon bringing the amino acid into its proper place When the next amino acid is in place, the two are joined in a condensation reaction The process is repeated until a stop code is read and a complete protein is formed

G. Mutation- change in the genetic code 1. Gene Mutation or Point Mutation- a nucleotide base is added, subtracted or changed to produce a change in the amino acid sequence of a protein

Genetic Code with RNA Codons

Proline Glutamic Acid Glutamic Acid A change in a single base in the DNA strand will result in a change in the m-RNA strand and the resulting protein Normal Hemoglobin Amino Acids DNA RNA 5 6 7 GGA CTC CTC CCU GAG GAG Proline Glutamic Acid Glutamic Acid Sickle Cell Hemoglobin Proline Valine Glutamic Acid GGA CAC CTC CCU GUG GAG

2. Chromosome Mutation- involves a change in many genes a) Deletion- part of a chromosome is lost b) Inversion- part of a chromosome is flipped around c) Translocation- part of a chromosome is added to another chromosome

3. Somatic & Germ Mutations a) Somatic mutations: change that occurs in body cells. Affects only the individual. Ie. cancer b) Germ Mutations- changed in the genetic code of gametes that will affect the individuals offspring 4. Mutagens- substances capable of causing damage to DNA 5. Most mutations are harmful

6. Frame Shift Mutations An insertion or deletion that results in the reading frame being shifted. All codons following the mutation will be changed. Example: THE RED DOG ATE THE CAT HER EDD OGA TET HEC AT