Griffith’s Experiments

Study suggested that DNA was probably the genetic material http://nortonbooks.com/college/biology/ani

mations/ch12a01.htm

http://www1.teachertube.com/viewVideo.php?video_id=113347&title=History_of_DNA

Hershey and Chase Experiments

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html

Hershey & Chase proved that DNA was the cell’s genetic material!

Radioactive 32P was injected into bacteria!

Protein coat labeledwith 35S

DNA labeled with 32P

bacteriophages infectbacterial cells

T2 bacteriophagesare labeled withradioactive isotopesS vs. P

bacterial cells are agitatedto remove viral protein coats

35S radioactivityfound in the medium

32P radioactivity foundin the bacterial cells

Which radioactive marker is found inside the cell?

Which molecule carries viral genetic info?

Hershey &

Chase

Chargaff

Discovered that amts of Adenine = Thymine, and Guanine = Cytosine

James Watson and Francis Crick

Double helix …..held together by hydrogen bonds

• DNA RNA

• 1. Sugar deoxyribose 1. Sugar ribose

• 2. Phosphate 2. Phosphate

• 3. Nitrogen base 3. Nitrogen base

• -thymine -uracil

Base Pairing

T A

G C

DNA Thymine (T) – Adenine (A)

Guanine (G) – Cytosine (C)

Weak hydrogen bonds

PURINE PYRIMIDINEPURINE PYRIMIDINE

PYRIMIDINE PURINEPYRIMIDINE PURINE

T or C A or G

9

DNADNA

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

Base Pairing

RNA Uracil (U) – Adenine (A)

Guanine (G) – Cytosine (C)

PYRIMIDINE PURINEPYRIMIDINE PURINE

PURINE PYRIMIDINEPURINE PYRIMIDINE

U A

G C

1. DNA unzips (hydrogen bonds between the nitrogen bases are broken by enzymes).

2. Free nucleotides pair with exposed bases. DNA Polymerase bonds the nucleotides together.

3. Two identical double stranded DNA molecules are formed. (ClassZone)

http://nortonbooks.com/college/biology/animations/ch12a04.htm

• 1. RNA is single stranded DNA is double

• 2. RNA can leave the nucleus and enter the cytoplasm DNA can not.

• 3. RNA has the sugar ribose, DNA has the sugar deoxyribose

• 4. RNA- uracil, DNA- thymine

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html

• 1. mRNA: messenger RNA, a copy of DNA from the nucleus.

• Reads DNA and copies it into RNA

T

A

C

DNA RNA

A

U

G

• 2. rRNA : ribosomal RNA, found on the ribosomes and functions in

attaching to mRNA to assemble the correct order of amino acids.

Binds to mRNA

Binds to tRNA

• 3. tRNA : transfer RNA, located in cytoplasm

• it picks up amino acids and like a factory worker it puts the correct amino acid in place to build a protein.

• Each tRNA has an anticodon on it that corresponds to the mRNA codon read off of the DNA.

A G U

Serine

U C A

tRNA

mRNA

(amino acid)

I. Transcription:1. DNA unzips with the help of RNA

Polymerase

2. mRNA reads the DNA, RNA Polymerase bonds the RNA nucleotides together.

3. mRNA breaks off and leaves thenucleus and travels to the ribosomes in the cytoplasm.

DNA strand TAC GCT TAG TTA ACTmRNA strand AUG CGA AUC AAU UGA

http://www.dnatube.com/video/3450/DNA-Transcription

http://www.dnatube.com/video/3446/BioRap-DNA-Replication-and-Protein-Synthesis-with-a-Beat

II. Translation:

1. mRNA attaches to ribosome. The ribosome reads 1 codon at a time. The process begins with a start codon.

2. tRNA with an amino acid finds its anticodon complement on mRNA’s codon.

mRNA : AUG UUU CCC CGA - codonstRNA : UAC AAA GGG GCU - anticodons

3. Ribosomes continue to read the codonsand another tRNA attaches leaving another amino acid.

4. Step 3 continues until the whole strand of mRNA is read, when the stop codon is reached the protein is completed.

http://www.biotopics.co.uk/genes/translation.html

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120077/micro06.swf::Protein Synthesis

Prokaryotic Transcription:

Operon – a region of DNA that contains a promoter, operator, and structural genes.

1. Promoter – DNA segment that allows a gene to be transcribed, RNA Polymerase binding site.

2. Operator – DNA segment that turns a gene “on” or “off”

*The lac operon was one of the earliest exps of gene regulation in bacteria

Lactose absent

Lactose present

http://www.biologycorner.com/bio4/notes/gene-expression.php

http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html

http://pages.csam.montclair.edu/~smalley/LacOperon.mov

– The lac operon is “off” when lactose is not present.

– The lac operon is “on” when lactose is present.

Eukaryotic Transcription:

*Transcription is controlled by regulatory DNA sequences andprotein transcription factors.

– Most eukaryotes have a TATA box promoter.– Enhancers and silencers speed up or slow down the rate

of transcription.

3 Steps1. Addition of the cap 2. Addition of the tail 3. Removal of introns with the splicing together of exons

Exons - code for parts of the protein

Introns – nucleotides that occur between exons

http://nortonbooks.com/college/biology/animations/ch13a05.htm

Gene mutations: a change in the sequence of nucleotides within a gene.

When do mutations occur? - most often during DNA replication.

Different Types (pg 253 Fig 8.20)

1. Point Mutations- 1 nucleotide is changed to another, thus coding for a different amino acid. Single base pair substitution.

2. Frameshift mutations- add or delete a nucleotide to cause the other bases to move up or down the DNA molecule.

http://nortonbooks.com/college/biology/animations/ch12a05.htm

http://nortonbooks.com/college/biology/animations/ch13a08.htm

(Change in chromosome structure)

Different Kinds 1. Deletion: when part of a chromosome is left out. 2. Insertion: part of a chromosome breaks off and inserts into

another causing a duplication in the other chromosome.

3. Inversion: genes break off and are reinserted backwards 4. Translocation: genes break off and add to a different

chromosome.(pg 253)

Causes: mutations are random events. Most often though environmental factors play a huge role in gene mutations

Read p254-255 and answer Apply Q on p254, and Summarize Q on p255

*Many chromosome mutations result when chromosomes fail to separate properly during meiosis.

Nondisjunction - occurs when homologous chromosomes or sister chromatids fail to separate.

Causes: Down syndrome, Turners syndrome, Klinefelters syndrome, cancer, etc.

http://www.biology.iupui.edu/biocourses/N100/2k2humancsomaldisorders.htmlhttp://www.pbs.org/wgbh/nova/body/

rnai.html NOVA video (RNAi)

http://www.teachersdomain.org/asset/lsps07_vid_rnai/

copyright cmassengale

• DNA is made up of a long chain of nucleotides.• Each nucleotide has three parts.

– a phosphate group– a deoxyribose sugar– a nitrogen-containing base

phosphate group

deoxyribose (sugar)

nitrogen-containingbase

http://www.sumanasinc.com/webcontent/animations/molecularbiology.html