CHAPTER 12 DNA & RNA. Griffith & Transformation Discovered transformation using bacteria that causes...
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Transcript of CHAPTER 12 DNA & RNA. Griffith & Transformation Discovered transformation using bacteria that causes...
CHAPTER 12
DNA & RNA
Griffith & Transformation
Discovered transformation using bacteria that causes pneumonia
Transformation Process in which part of the nucleotide sequence of
DNA is copied into a complementary sequence in RNA
Avery & DNA
Retested Griffith’s experiment to determine what caused transformation
Discovered that the nucleic acid in DNA stores and transmits the genetic information from one generation of an organism to the next
Hershey-Chase Experiment
Studied virusesConcluded that DNA was the genetic material
of bacteriophages, not protein
Components & Structure of DNA
• DNA is made up of Nucleotides• Each nucleotide is made up of 3 basic
components:– 5 carbon sugar (deoxyribose)– A phosphate group– Nitrogenous base
• 4 nitrogen bases– Adenine– Guanine– Cytosine – thymine
Chargaff’s Rule
The observation that [A] = [T] & [G] = [C]Found that in 4 different types of organisms
the amount of A & T were nearly the same as well as the amount of G & C were nearly the same.
Double Helix
• Watson & Crick built a 3-D model of DNA based on the evidence found by Franklin using X-ray.
• Found that DNA was a double helix, in which two strands were wound around each other resembling a spiral staircase
• Hydrogen bonds hold the two strands together but only formed between A&T and G&C
• This is called base pairing
12-2 Chromosomes & DNA Replication
DNA Replication
Each strand of the DNA double helix has all the information needed to reconstruct the other half by the mechanism of base pairing.
Replications proceeds in both directions until each chromosome is completely copied
Duplicating DNA
Before a cell divides it duplicates DNADuring duplication, the DNA molecule
separates into 2 strands, produces 2 new complementary strands based on base pairing.
How Replication Works
Replication is carried about by many enzymes, the principle enzyme is DNA polymerase It joins individual nucleotides to produce a DNA
molecule Proofreads each new DNA strand
12-3 RNA & Protein Synthesis
The Structure of RNA
Consists of a long chain of nucleotides3 main differences between RNA & DNA
The 5 carbon sugar is ribose, not deoxyribose RNA is generally single stranded RNA contains uracil instead of thymine
Types of RNA
RNA has many functions, but in the majority of cells most RNA molecules are involved in only one thing – PROTIEN SYNTHESIS
3 main types of RNA Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA)
Types of RNA
Genes contain instructions for assembling amino acids into proteins
RNA molecules that carry copies of these instructions are known as mRNA
Proteins are assembled on the ribosomes. Ribosomes are made up of several dozen proteins as well as a form of RNA called rRNA
During protein construction, a third type of RNA molecule transfers each amino acid to the ribosome as it is specified by coded messages in mRNA. This is known as tRNA.
Transcription
RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA. This is called transcription.
Requires RNA polymeraseRNA polymerase binds to DNA and separates
the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.
RNA Editing
DNA of eukaryotic genes contains sequences of nucleotides called introns that are not involved in coding for proteins.
The DNA sequence that code for proteins are called exons because the are expressed in the synthesis of proteins.
When RNA molecules are formed they copy both the introns and exons.
The Genetic Code
The language of mRNA instructions is called the genetic code.
A codon consists of 3 consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide
There are 64 possible the base codonsDuring translation, the cell uses information
from mRNA to produce proteins
Mutations & Gene Regulation
Kinds of Mutations
Mutations are changes in the genetic material
Point Mutations = gene mutations involving changes in one or few nucleotides Include:
Substitutions Insertions Deletions
Frameshift Mutations = shift the “reading frame” of the genetic message
Examples
PointThe fat cat ate the wee rat.The fat hat ate the wee rat.
FrameshiftThe fat cat ate the wee rat.The fat caa tet hew eer at.
Chromosomal Mutations
Involve changes in the number or structure of chromosomes
May change locations of genes on chromosomes
4 types Deletions Duplications Inversions Translocations
Examples
OriginalOriginalABCDEFABCDEF
Deletions ACDEF
Duplications ABBCDEF
Inversion AEDBBF
Translocations ABCJKL GHIDEF