DNA and RNA Chapter 12 Hereditary Material Genes are protein codes. Our genes are on our...
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Transcript of DNA and RNA Chapter 12 Hereditary Material Genes are protein codes. Our genes are on our...
Hereditary MaterialHereditary Material
• Genes are protein codes.
• Our genes are on our chromosomes.
• Chromosomes are made up of DNA.
• Genes are composed DNA!
Chromosome StructureChromosome Structure
• Chromatin is tightly coiled around proteins called histones.
• DNA and histone molecules form a beadlike structure: nucleosome
• Nucleosomes create the supercoils
of DNA in a chromosome.
Structure of DNA• In eukaryotes, DNA is found in the
NUCLEUS of cells.• DNA is made up of a series of monomers
called nucleotides.Nucleotide structure:
1. 5–carbon sugar: Deoxyribose2. Phosphate group3. Nitrogenous base
• DNA is a twisted-ladder called a
DOUBLE HELIX!
DNA NucleotideDNA Nucleotide
OO=P-O O
PhosphatePhosphate GroupGroup
NNitrogenous baseNitrogenous base (A, G, C, or T)(A, G, C, or T)
CH2
O
C1C4
C3 C2
5
SugarSugar(deoxyribose)(deoxyribose)
Nitrogenous BasesNitrogenous Bases
• Double ring Double ring PURINESPURINESAdenine (A)Adenine (A)Guanine (G)Guanine (G)
• Single ring Single ring PYRIMIDINESPYRIMIDINES
Thymine (T)Thymine (T)Cytosine (C)Cytosine (C) T or C
A or G
Chargaff’s (Base Pairing) Chargaff’s (Base Pairing) RuleRule
• AdenineAdenine must pair with ThymineThymine
• GuanineGuanine must pair with CytosineCytosine
• The bases form weak hydrogen bonds
G CT A
Why do they pair together
this way?
DNA Double HelixDNA Double Helix
NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)
““Rungs of ladder”Rungs of ladder”
““Legs of ladder”Legs of ladder”
Phosphate &Phosphate &Sugar BackboneSugar Backbone
Hydrogen bonds
Nucleotide
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
DNA Structure
DNA Replication
• Occurs during cell division.
• Helicase enzyme “unzips” the molecule of DNA, breaking the hydrogen bonds.
• Free-nucleotides in the nucleus will be bonded with its complementary base.
• DNA polymerase helps to bond the nucleotides together and check for errors.
DNA ReplicationSection 12-2
Growth
Growth
Replication fork
DNA polymerase
New strand
Original strand DNA
polymerase
Nitrogenous bases
Replication fork
Original strand
New strand
The Scientists
• Griffith – one strain of bacteria was “transformed” into another strain.
• Avery – found that DNA was the transforming factor.
• Hershey and Chase – DNA is the genetic material.
• Watson and Crick – discovered the molecular structure of DNA.
Bacteriophage with phosphorus-32 in DNA
Phage infectsbacterium
Radioactivity inside bacterium
Bacteriophage with sulfur-35 in protein coat
Phage infectsbacterium
No radioactivity inside bacterium
Section 12-1Hershey-Chase Experiment
Chargaff and Franklin• Chargaff
Percentages of guanine and cytosine bases are almost equal in any sample of DNA
Same is true of adenine and thymine
DNA in all instances and from all organisms followed this rule
• Rosalind FranklinX-Ray diffraction showed that
DNA was twisted into a
double helix.
RNARNA
• Long, single strand of nucleotides.
• Nitrogen bases: A,U,G,C no Thymine!
• Sugar: Ribose
• Found in cytoplasm and nucleus
• Types: messenger, transfer, ribosomal
• Function: Involved in the synthesis of protein molecules.
TranscriptionTranscription• Location where it occurs: Nucleus
• RNA polymerase will unwind DNA at the region to be transcribed.
• It locates and binds at the promoter.
• mRNA is then made by base-pairing:
A-U, G-C, T-A, C-G If DNA sequence is: GATTACA
Then mRNA sequence is: CUAAUGU
• When finished, mRNA leaves the nucleus and goes to the cytoplasm.
RNADNA
RNApolymerase
TranscriptionSection 12-3
Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)
TranslationTranslation
Location: Cytoplasm mRNA finds a ribosome
Ribosome reads strand for the start “codon”A codon is a mRNA triplet. Ex: AUG, UUC, etc
Start codon is: AUG
Transfer RNA’s bring
amino acids to
ribosome.
• tRNA’s anticodon bonds with mRNA codon.
mRNA codons AUG UAA CGC
tRNA anticodons UAC AUU GCG
• Amino acids connected with peptide bonds.
• When a “Stop” codon is reached. Protein is released from ribosome.
Translation continued…Translation continued…
How to Interpret m-RNA’s Code:
• Each 3 nitrogen base sequence is called a CODON.
• Each codon specifies for a particular amino acid.
• AUG codon starts the initiation of the protein and codes for the amino acid methionine.
• Stop codons do not code for any amino acids ending the protein chain.
• A polypeptide is a chain of amino acids joined with peptide bonds – aka a PROTEIN!
Let’s Practice!Let’s Practice!
DNA: TACTTGGAT
mRNA: AUGAACCUA
tRNA: UACUUGGAUAmino Acid squence:
Methionine, Asparagine, Leucine
MutationsMutations
• Changes that occur in the DNA
• Two types:
1. Gene mutations
2. Chromosomal mutations
• Many mutations are harmless
• Pros: increase adaptation or survival
• Cons: some can be lethal or debilitating
Gene MutationsGene Mutations
• Changes that occur in a single gene.
• Point mutations: one nucleotide that affects one amino acid.
(substitutions produce point mutations)
• Frameshift mutations: involve the reading of the DNA or m-RNA strand; many amino acids are affected. (insertion or deletions produce frameshift mutations)
Chromosomal MutationsChromosomal Mutations
• Whole chromosome is affected.
• Four types:
1. Deletion – loss of material
2. Duplication – addition of material
3. Inversion – rearrangement of material
4. Translocation – switching material with another chromosome