dna & rna units of life

DNA & RNAUnits of Life

A. History of DNAB. DNA DiscoveryC. RNAD. TranscriptionE. TranslationF. Mutations

DNA: Blueprint for Life

A.History of Discovery1. Frederick Griffith: Mice

Transformation2. Avery: DNA Identified3. Hershey-Chase: DNA and Viruses4. Rosalind Franklin: X-ray Evidence5. Chargaff’s Rules: Base Pairing6. Watson and Crick:The Double Helix

Discovery of DNA: A History

FREDERICK GRIFFITH (1928)• Studied way in which bacteria

cause pneumonia and recognized process of transformation.

• Showed through experiments that one strain of bacteria could be transformed into another.

• Hypothesized that there was a transforming factor involved.

Griffith’s Experiment

Disease-causing bacteria (smooth

colonies)

Harmless bacteria (rough colonies)

Heat-killed, disease-causing bacteria (smooth colonies)

Control(no growth)



Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

Dies of pneumonia

Section 12-1

Griffith’s Experiment

Disease-causing bacteria (smooth

colonies)

Harmless bacteria (rough

colonies)

Heat-killed, disease-causing bacteria (smooth

colonies)

Control(no growth)



Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

Dies of pneumonia

Section 12-1

DNA Discovery: A History

AVERY (1944)• Repeated Griffith’s experiments

and identified DNA as the transforming factor-identified DNA

• DNA-stores and transmits genetic information from one generation to another.


HERSHEY-CHASE (1952)• Experiments with bacteria-

killing viruses (bacteriophages)• Confirmed again that DNA was

the molecule that contained the genetic code.

Hershey-Chase Experiment

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium


ROSALIND FRANKLIN and MAURICE WILKINS (1950’S)

• Studied DNA molecule by using a purified DNA sample and x-ray pictures of molecule.

• Found it was a twisted “X” structure.


ERWIN CHARGAFF (early 1950’s)

• Observed in any DNA sample, the number of adenine molecules was equal to the number of thymine; same for guanine and cytosine.

• Developed nitrogen base pairing rules

Percentage of Bases in Four Organisms

Source of DNA A T G CSource of DNA A T G C

Streptococcus 29.8 31.6 20.5 18.0

Yeast 31.3 32.9 18.7 17.1

Herring 27.8 27.5 22.2 22.6

Human 30.9 29.4 19.9 19.8

Streptococcus 29.8 31.6 20.5 18.0

Yeast 31.3 32.9 18.7 17.1

Herring 27.8 27.5 22.2 22.6

Human 30.9 29.4 19.9 19.8


WATSON-CRICK (1953)• Tried to build 3D DNA model -

couldn’t quite solve it• Used Franklin’s pictures to

develop the double helix model• Double helix model explained

much about DNA structure, including placement of nitrogen bases and the formation of bonds.

• Received Nobel Prize along with Wilkins (Franklin didn’t—why?)

DNA: Blueprint for Life

B. The Structure of DNA1. Nucleotides – basic unit of DNA2. Nitrogen Bases3. DNA Replication

Structure of DNA

DNA made of nucleotides, the basic unitNucleotide is made of three parts:1. One Phosphate2. One 5-Carbon Sugar (deoxyribose)3. One Nitrogen base

Adenine(A), Guanine(G) – Purines Thymine(T), Cytosine(C) – Pyrimidines

Structure of DNA

Sugar and Phosphate are the “backbone” of DNA

Two parallel strands of sugar-phosphate groups with pairs of nitrogen bases linking the two strands together with weak hydrogen bonds, forming a double helix.

WHY WEAK BONDS?

Structure of DNA

Nitrogen Base Pairing ‘Rulz’:A=T (one purine/ pyrimidine)C=G (one purine/ pyrimidine)

DNA strands are complementary because of base pairing rules

Nitrogen bases attached to sugars.

DNA NucleotidesPurines Pyrimidines

Adenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

Structure of DNA

Weak Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

DNA Replication

A Perfect Copy When a cell divides, each daughter

cell receives a complete set of chromosomes. This means that each new cell has a complete set of the DNA code. Before a cell can divide, the DNA must be copied so that there are two sets ready to be distributed to the new cells.

DNA Replication

Complementary strands of DNA serve as a pattern for a new strand.

DNA replication carried out by enzymes which “unzip” the two strands by breaking the hydrogen bonds.

Then, appropriate nitrogen bases are inserted. Enzymes also proofread the bases to make sure of correct base pairing.

Chromosome Structure

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

DNA Replication

DNA Replication

DNA G C C A T T G T A A T Copied DNA C G G T A A C A T T A

enzymes

Copied DNA C G G T A A C A T T A

DNA G C C A T T G T A A T

RNA: The Other Code

C. RNA and Protein SynthesisA.The Structure of RNAB. DNA and RNA

Similarities/DifferencesC. TranscriptionD. Types of RNAE. Protein SynthesisF. Translation

RNA: The Other Code

A. RNA similar to DNA• long chain made of nucleotides• each nucleotide consists of:

a sugar a phosphate a nitrogen-containing base

• sugar and phosphate still backbone

of RNA

RNA: The Other Code

B. RNA different from DNA• Different type of sugar (ribose)• Single strand rather than a double strand RNA molecule is a disposable copy of DNA• Nitrogen base THYMINE found in DNA replaced by a similar base URACIL (U) in RNA

ex. ( A - U ) and ( C - G )

Why RNA?

C. Why does DNA need to transfer genetic information to RNA?

1. DNA is found in the nucleus. Ribosomes are outside the nucleus.

2.DNA does not leave nucleus-too large for nuclear pores.

3.Messenger must bring genetic information from the DNA to the ribosomes to make proteins/amino acid

4.Special molecule, messenger RNA (mRNA), performs this task.

RNA: The Other Code

RNA - The Other Part of the CodeA.RNA –“messenger” between

the DNA in the nucleus and the ribosomes. (mRNA)

B.Ribosomes –organelles outside the nucleus that make proteins from amino acids.

C. Proteins/Amino Acids –used to build and repair cells.

RNA Synthesis

Transcription- process by which one strand of DNA is copied into a complementary strand of mRNA in the nucleus.

DNA G C C A T T G T A A TCopied DNA C G G T A A C A T T A

mRNA C G G U A A C A U U A

mRNA G C C A U U G U A AU

enzymes

enzymes

enzymes

Transcription

RNADNA

RNApolymerase

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

Types of RNA

Transfer RNA (tRNA)A. Carries amino acids to ribosome B. Single strand looped back on itselfC. Anticodon-three nucleotides on tRNA

are complementary to the three on the mRNA.

D. Matching of codon (mRNA) to anticodon (tRNA) allows the correct amino acid to be put in place.

Ribosomal RNA (rRNA)A. makes up majority of ribosome

Types of RNA

from to to make up

also called which functions to also called also called which functions towhich functions to

can be

RNA

Messenger RNA Ribosomal RNA Transfer RNA

mRNA Carry instructions rRNACombine

with proteins tRNABring

amino acids toribosome

DNA Ribosome Ribosomes

Protein Synthesis

A. Nucleotides in DNA have all the information to make proteins.

B. DNA code copied into mRNAC. Proteins are made of amino

acids which are coded from mRNA.

D. mRNA code is read in triplet form called a CODON which specifies certain amino acids using a decoder (p.201)

Protein Synthesis: Translation

Only 20 amino acids make all life as we know it! How can this be?

*AUG - codes for amino acid methionine or be an “initiator codon” and will always start mRNA

*Some are “stop” codons which end mRNA

Translation -the decoding of mRNA code into an amino acids--proteins

TranslationMessenger RNA

Messenger RNA is transcribed in the nucleus.

Transfer RNA

The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon.

mRNA Start codon

Ribosome

Methionine

Phenylalanine tRNALysine

Nucleus

mRNA

Translation (continued)

The Polypeptide “Assembly Line”The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids.

mRNARibosome

Translation direction

Lysine tRNA

tRNA

Ribosome

Growing polypeptide chain

mRNA

Completing the PolypeptideThe process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

The Genetic Code Decoder

BACK

Translation

DNA T A C T T T G T A A C TmRNA A U G A A A C A U

U G A

enzymes

Determining the Sequenceof a Gene

•DNA contains the code of instructions for cells. •Sometimes, an error occurs when the code is copied. •Such errors are called mutations.

Mutations

• Mutations can occur on individual chromosomes by way of gene mutations.– Base sequence gets rearranged

and may cause insertion, deletion, or substitution of genes

• Mutations can also occur with entire chromosomes.

Gene Mutations:Substitution, Insertion, and

Deletion

Substitution InsertionDeletion

• Original The fat cat ate the wee rat.

• Point Mutation The fat hat ate the wee rat.• Frame Shift The fat caa tet hew eer at.• Deletion The fat __ ate the wee rat.• Insertion The fat cat xlw ate the wee rat• Inversion The fat tar eew eht eta tac.

Chromosome Mutations

Deletion

Duplication

Inversion

Translocation

Mutagen.

• Ultraviolet light, nuclear radiation, and certain chemicals can damage DNA by altering nucleotide bases so that they look like other nucleotide bases

Environmental Impact

• Ultraviolet light, nuclear radiation, and certain chemicals can damage DNA by altering nucleotide bases so that they look like other nucleotide bases.

Mutagens are environmental agents that can cause mutations in the genetic code.

• High energy radiation from radioactive elements, X-rays, gamma rays, microwaves, and ultraviolet light (please use sunscreen and wear a hat).

• Industrial chemicals such as PCB's (support the ban).

• Pollutants such as cigarette smoke (please don't smoke and if you do work hard to quit)

• Pesticides (eat organic).

• Food Additives (read food labels).

• Drugs (use only when necessary).

• Viruses (wash your hands and practice safe sex).

Mutagen

• An agent, such as a chemical, ultraviolet light, or a radioactive element, that can induce or increase the frequency of mutation in an organism.

• Spontaneous DNA replication and repair errors, spontaneous modification of nucleotides

• All types of mutations produced UV irradiation

• Pyrimidine dimers induce error prone repair (SOS) Mainly G-C to A-T transitions, but all other types of mutations including deletions, frameshifts, and rearrangements

Impact of Genetics

caused by

includeincludeinclude

AutosomeDisorders

Recessive alleles

Dominant allelesCodominant

alleles

Albinism Galactosemia Tay-Sachs disease

Huntington’s disease

Sickle cell disease

Cystic fibrosis

Phenylketonuria AchondroplasiaHypercholes-

terolemia

Pedigrees

A completely shaded circle or square indicates that a person expresses the trait.

A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait.

A half-shaded circle or square indicates that a person is a carrier of the trait.

A horizontal line connecting a male and female represents a marriage.

A circle represents a female.

A square represents a male.

A vertical line and a bracket connect the parents to their children.

Blood Groups

A. Four major blood groups: A, B, O, AB

B. Each type carries certain AntigensC. Antigens are markers on surface of

cells that identify the type of cell. Allows antibodies to attack if they aren’t identified correctly.

D. Antibodies found in the body, they provide protection from diseases and foreign substances. As you are exposed to diseases, your body builds up antibodies—resistance.

Blood GroupsE. Blood Type Antigen Antibodies A A b

B B aAB AB noneO none a and b

F. Type O blood is the universal donor blood Why?

There are no markers (but O can only receive O)

G. Type AB is the universal recipient blood Why?

Carry both markers; lack antibodies

Blood Groups

Phenotype(Blood Type Genotype

Antigen on Red Blood Cell

Safe Transfusions

To From

Blood Groups-Rh Factor

• Rh factor identified in rhesus monkey and later found in human blood.

• Rh+ is dominant over Rh-

• If you have Rh+ blood (O+, A+, etc)= O+O+, A+O- , B+O+, etc

• If you have Rh- blood (O-, B-, etc)=

O-O-, B-O- ,A-O- , etc

Blood Types-Rh Factor• Blood types must match up

correctly when getting blood or death results.

• Important during pregnancy: if mom is Rh- and has Rh+ fetus, mom’s antibodies don’t recognize Rh+ and begin to attack. Could result in death. This can be detected early and treated with blood supplements.

• What was the dad’s Rh type?

NondisjunctionHomologous

chromosomes fail to

separate

Meiosis I:Nondisjunction

Meiosis II

Sex-Linked Traits: Colorblindness

Father(normal vision)

ColorblindNormal vision

Mother (carrier)

Daughter(normal vision)

Son(normal vision)

Daughter(carrier)

Son(colorblind)

Male

Female

dna & rna units of life

Documents

strain of bacteria

dna structure

dna identifiedhersheychase

bacteria cause pneumonia

sstudied dna molecule

double helixdiscovery

purified dna sample

d dna model