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