DNAChapter 12

DNA

Holds our genetic information Like a library

Important for mitosis to occur

Biologists had to discover the chemical nature of DNA to determine that it is responsible for our genetic information

Griffith and Transformation

Transformation: when a strain of bacteria is changed by a gene or genes from another bacteria

Experiment Inject mice with bacteria containing virus for

pneumonia Smooth colonies = have bacterial infection Rough colonies = harmless bacteria

Griffith and Transformation If the virulent colonies were killed with heat and mixed

with harmless bacteria, then the harmless bacteria get transformed into virulent bacteria

Some factor of the bacteria was tranformed to harmless bacteria

Avery and DNA

Wanted to repeat Griffith’s experiment

Treated heat-killed virulent bacteria with enzymes One enzyme destroyed RNA and proteins Another enzyme destroyed ONLY DNA

Lethal Virus

Avery and DNA

Results showed that bacteria treated with DNA destroying enzyme did not transform harmless bacteria into virulent bacteria

It is the DNA that stores the genetic information from one generation to the next

Lethal Lethal Non Lethal

Lethal Virus

Hershey-Chase

Bacteriophage: a virus that infects bacteria ONLY

Scientists wanted to see what gets injected into a bacteria to cause infection Used a radioactive

marker for DNA and protein

Hershey Chase After infection, the bacteria that had radioactive marker

on DNA showed that it is the DNA that is inserted into the bacteria

Results: DNA from the virus is what causes infection

DNA Structure

Monomer of DNA is a nucleotide 5-carbon sugar Phosphorous group Nitrogenous base

4 Nitrogenous bases in DNA Adenine Guanine Thymine Cytosine

DNA Structure

Backbone of DNA is the sugar and phosphate

Nitrogenous bases stick out of side to form latter rungs These bases are

repeated in a pattern that form our genetic code

DNA Structure

Chargaff’s Rule Scientist that discovered a pattern between the 4

bases Same percentage of Adenine as Thymine Same percentage of Guanine as Cytosine

Scientists still not sure how they match up though

DNA Structure

Rosalind Franklin Scientist that worked with X-ray diffraction Used X-rays on a portion of DNA and the results

showed an X pattern

DNA Structure

Watson & Crick Scientists that

were able to understand Rosalind’s X-ray picture

Result: DNA has a double helix pattern where the nitrogenous bases face each other

DNA Structure

DNA has a double helix pattern Looks like a ladder twisted up

The sides of the ladder are the sugar and phosphate and the rungs of the ladder are the nitrogenous bases paired up

The adenine binds to thymine

The guanine binds to cytosine

This concluded Chargaffs’s rule base pairing

DNA and Chromosomes

Prokaryotes Lack nucleus and organelles DNA floats as a circle in the

cytoplasm

Eukaryotes 1000 times more DNA than

prokaryotes DNA is located in nucleus Specific number of

chromosomes Ex: Humans have 46

chromosomes

DNA and Chromosomes DNA Length

DNA is very long DNA is coiled up into a

very small space because it is in chromatin form

Chromosome Structure Tightly packed

chromatin is wrapped around small proteins called histones

When chromatin gets super coiled you create a chromosome

DNA Replication

Each strand of DNA is needed to be a template for a new strand of DNA to be produced

Since you can use one strand to make the other side, they are said to be complementary

Duplicating DNA

Before mitosis occurs, DNA needs to be duplicated first during interphase

When DNA duplicates, its called replication

DNA molecules separates into two strands, then produces two new complementary strands following the rules of base pairing

Each strand serves as a template for the new strand

How Replication Occurs Enzymes help make new strands of DNA

One enzyme called helicase “unzips” the DNA, separating the base pairs

DNA polymerase adds new bases to pair up with the template

This enzyme also proofreads to make sure everything matches

What would be the matching bases to the part of DNA shown below?

RNA & Protein Synthesis

Sections 3-4

Structure of RNA

Made of nuleotides

Three differences between DNA & RNA Sugar

DNA = deoxyribose sugar RNA = ribose sugar

RNA is single stranded RNA uses Uracil instead of

Thymine to bond with Adenine

Types of RNA

Three types of RNA mRNA

Messenger RNA rRNA

Ribosomal RNA tRNA

Transfer RNA

Types of RNA

Messenger RNA This is a copy of complimentary strand of DNA Eventually will code for a protein to be made

Types of RNA

Ribosomal RNA RNA found in ribosomes (organelles in the cell) Ribosomes are the factory for protein synthesis

Types of RNA

Transfer RNA Help produce a protein from mRNA Brings amino acids (monomer of protein) to

ribosome to bond them together and make a whole protein

Transcription

Taking DNA and making an RNA copy Occurs in the cell’s nucleus RNA polymerase opens the DNA and adds RNA

copy to the template Once this is made it is called pre-mRNA

RNA Editing Pre-mRNA is a rough draft to the final copy of

mRNA Some parts of pre-mRNA are not needed to make

a protein These unnecessary parts are called introns Introns get cut out of pre-mRNA

Before leaving the nucleus, mRNA needs to get a cap and tail to finalize the RNA strand

The Genetic Code Proteins are made of 20 possible amino acids In order to make a protein from a strand of mRNA, the

mRNA is read in a 3 letter sequence called codons

The Genetic Code

Each three letter codon represents an amino acid DNA = AGCGTGCCA RNA = Codons = Amino acids =

The Genetic Code

RNA knows when to start and stop based on the codons read There is ONE start codon: AUG There are THREE stop codons: UAA, UAG, UGA

Translation

Taking mRNA and making a protein

Occurs in the cytoplasm on a ribosome

tRNA brings specific amino acids to ribosome If mRNA = AUG, then tRNA = UAC The tRNA has the anti-codon

Translation As new tRNA brings amino acids to the ribosome, past

ones break off leaving just amino acids bonded to each other

This continues until one of the three STOP codons is met Finished amino acid strand goes through protein folding

Mutations

Changes in the DNA sequence that affect the cell

Two types of mutations Gene mutation Chromosomal mutation

Gene Mutation

Point mutation A change in one nucleotide in a DNA

sequence Occur only in a single point of the DNA Can sometimes be a problem

Frameshift mutation A change in the reading frame of DNA Since DNA is read in 3 letter codons, if

there is an insertion, deletion, or large change in these codons the frame is changed

Chromosomal Mutation A change in the number of chrom0somes in the

cell

Four types Duplication Deletion Inversion Translocation