11.1 Genes are made of DNA
Griffith Experiment
Avery Experiment
-Destroyed proteins
-Mice still died with mix
Hershey Chase Experiement
• Virus- nucleic acid wrapped in protein; needs host to reproduce
• Bacteriophage- virus that infects bacteria
Hershey Chase Experiment
Question 1 & 2
1. Explain how experiments done by Griffith, Avery & Hershey and Chase supported that genes are made of DNA? [4 points]
2. Identify the parts of DNA and how the double helix is put together (bases)? [4 points]
11.2 Nucleic acids store information in their sequences of
chemical units
DNA into chromosomes
Nitrogenous Bases
DNA- structures
Rosalind Franklin & Maurice Wilkins
1950’s photographs of the DNA molecule using X-ray crystallography which showed the shape to be a helix
Erwin Chargaff
• 1951, proved that the % of A = T and % of G = C
Watson &Crick
• 1953, used data from the other scientists and built models to finally figure out the exact structure of DNA
• 1962 won the nobel prize in Medicine
11.3 DNA replication is the molecular mechanism of
inheritance
DNA Replication
DNA Replication• Enzymes are protein molecules that
catalyze chemical reactions in a cell – usually any protein ending in “ase” is an enzyme
• Helicase- unwinds DNA• DNA Polymerase 3 () - Adds
complementary nucleotide• DNA Polymerase 1 ()- Checks for
error• Single strand bind proteins- help hold
open DNA
DNA Replication
• DNA primase- makes an initiation (starting) site for replication
• RNA primer- short segment of RNA where DNA replication starts
• DNA ligase- binds two nucleotides together
• Topoisomerase (gyrase)- relaxes and recoils helix
DNA Replication
11.4 A gene provides the information for making a specific
protein
DNA & RNA• Deoxyribose
sugar
• A,T,C,G
• Double strand
• Stays in Nucleus
• DNA
• Ribose sugar• A,U,C,G • Uracil pairs with
adenine• Single strand• Nucleus to cytoplasm• Messenger (mRNA),
transfer (tRNA), ribosomal (rRNA)
Types of RNA• mRNA - Messenger RNA: Encodes amino acid sequence of a
polypeptide.
• tRNA - Transfer RNA: Brings amino acids to ribosomes during translation.
• rRNA - Ribosomal RNA: With ribosomal proteins, makes up the ribosomes, the organelles that translate the mRNA.
•• snRNA - Small nuclear RNA: With proteins, forms complexes that are used in RNA processing in eukaryotes. (Not found in prokaryotes.)
DNA & RNA
Beadle and Tatum
• Beadle and Tatum discovered when looking at mutant Neurospora crassa (bread mold)
• Individual gene produces a specific enzyme
• One gene - one polypeptide (combinaiton of amino acids)
DNA to Protein
Table of Codons
11.5 There are two main steps from genes to proteins
Transcription: Base Pairing of mRNA with DNA
RNA Transcription
Steps of Transcription
1. DNA double helix unwound and separated by RNA polymerase
2. RNA polymerase adds RNA nucleotides together, making a single strand of mRNA which is complementary to 1 strand of the DNA
Steps of Transcription
3. mRNA is processed (modified) before leaving the nucleus
a. introns (non coding regions) are cut out of the mRNA
b. exons (coding regions) are “spliced” together to form the
final mRNA product
4. Introns are cut out and exons are spliced together to form the final copy of messenger RNA (mRNA)
RNA editing
• Most eukaryotic protein-coding genes contain segments called introns, which break up the amino acid coding sequence into segments called exons.
The transcript of these genes is the pre-mRNA (precursor-mRNA).
The pre-mRNA is processed in the nucleus to remove the introns and splice the exons together into a translatable mRNA. That mRNA exits the nucleus and is translated in the cytoplasm.
Transfer RNA (tRNA)
Adding Amino Acids to a
Polypeptide Chain
Initiation Translation
Elongation Translation
Termination Translation
Steps of Translation
1. mRNA leaves the nucleus and is transported to the ribosome where translation takes place
2. Ribosome holds onto the mRNA, the mRNA codon AUG is located in the P site of the ribosome
3. tRNA carries an amino acid to the P site of the ribosome
4. Another tRNA carries the next amino acid to the A site of the ribosome
Steps of Translation
5. Two amino acids are joined together with a peptide bond
6. tRNA in the P site leaves7. Ribosome moves along the mRNA until the
next codon is located in the A site (the tRNA which was located in the A site
is now in the P site and is holding the peptide chain)
8. tRNA carries the next amino acid to the A site
Steps of Translation
9. New amino acid is joined to the peptide chain (the polypeptide is made of 3 amino acids)
10. tRNA in the P site leaves
11. Process continues until a stop codon appears in the A site of the ribosome
12. Polypeptide is now complete
Rules for translation
1. Codon is a three-base “word” that codes for one amino acid
2. Determine the amino acid coded for by an mRNA codon use the genetic code
3. Genetic code is universal – all species use the same genetic code, the same 20 amino acids are used in all living organisms
Summary of Translation Process
11.6 Mutations can change the meaning of genes
Point vs. Frameshift Mutations
Chromosome Mutations
How mutations affect genes1. A mutation is any change in the nucleotide
sequence of DNA.2.Two categories of mutations
a. Base substitutions (point)– replacement of one nucleotide with another
i. This can change the protein or not change the protein
b. Base insertions or base deletions (frameshift) – addition of an extra nucleotide or subtracting a nucleotide
i. Have more effect on the protein than a substitution
What causes mutations?
1. Mistakes during DNA replication can cause mutations
2. Mutagens – physical or chemical agents that cause mutationsa. Physical mutagens – high energy radiation, X-
rays, Ultraviolet lightb. Chemical mutagens – chemicals that are
similar to DNA bases and cause incorrect base-pairing
Mutations Effects
Body Cells
• Cancers
Gametes
• Birth defects
• Genetic disorders
Ch. 11 Test
• Vocabulary• DNA & RNA structure• Replication, transcription, translation-
content and problems• Scientists & experiments involved• Mutations & mutagens- types and
effects
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