By the 1940’s, scientists knew that chromosomes carried hereditary material and consisted of DNA and proteins. Most thought proteins were the genetic material because it is a complex macromolecule and little was known about nucleic acids.

In 1928, Frederick Griffith was trying to determine how bacteria infected people.
He isolated two different strains of pneumonia bacteria
1. smooth strain (S) – polysaccharide coat, on the bacterial cell prevents attach by the immune system
2. rough strain (R) – polysaccharide coat is absent and therefore the immune system can kill the bacteria

Griffith performed four sets of experiments – Fig.
12-2
Experiment – injected live S strain into the mice;
Results – mice developed pneumonia & died
Conclusion – S strain causes disease
Experiment – injected live R strain into the mice:
Results – mice survived
Conclusion – R strain does not cause disease

Griffith performed four sets of experiments – Fig.
12-2
Experiment – injected heat killed S strain
Results – mice survived
Conclusion – polysaccharide coat does not cause pneumonia

Griffith performed four sets of experiments – Fig.
12-2
Experiment – Heat killed S strain cells mixed with the live R strain cells and then injected into mice
Results – mice died from pneumonia & blood samples from dead mice contained living S strain cells
Conclusion – R cells had acquired “some factor” to make polysaccharide coat

Transformation – the assimilation of external genetic material by a cell
The disease causing ability was inherited by the bacterial offspring, therefore information for disease might be located on a gene.

http://www.dnalc.org/view/16375-
Animation-17-A-gene-is-made-of-DNA-
.html
The above link is an explanation of Griffith’s &
Avery’s findings. Great site – please review. Avery discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next.

Bacteriophage – a virus that infects a bacterium; made up of DNA or RNA and a protein coat. – Fig. 12-3, 12-4

DNA – contains no sulfur but does have phosphorus
Proteins – contain almost no phosphorus but do have sulfur

Hershey & Chase performed two sets of experiments
1. T2 with radioactive phosphorus infects bacterium – 32P shows up in bacterial
DNA
2. T2 with radioactive sulfur infects bacterium – 35S does not show up in bacterial DNA
3. Conclusion – genetic material of T2 was DNA not protein

http://highered.mcgrawhill.com/olc/dl/120076/bio21.swf
(Hershey/Chase experiment animation)

Nucleotide – functional unit; composed of a phosphate group, sugar (deoxyribose), and a nitrogenous base
T- thymine A – Adenine
G – Guanine C – cytosine
Chargaff’s Rules – Fig. 12-6
[A] = [T] [C] = [G]

X-ray evidence – x shaped pattern shows
DNA strands are twisted and nitrogenous bases are in the center (Rosalind Franklin created this image which was used by
Watson & Crick to explain the structure of
DNA) She probably would have shared in the Nobel Peace Prize with them for this discovery if she had not died.

Prokaryotic Cells lack a membrane bound nucleus; only one circular chromosome holds most of the genetic material. Fig. 12-8

Eukaryotic cells have a membrane bound nucleus; chromosomes are found in pairs and the number is species specific
DNA is a very long molecule and must be a tightly folded
Chromatin – DNA & histone proteins make up a unit called a nucleosome Fig. 12-10

The two DNA strand separate
Each strand is a template for assembling a complementary strand.
Nucleotides line up singly along the template strand in accordance with the base-pairing rules ( A-T and G-C)
DNA polymerase links the nucleotides together at their sugar-phosphate groups.
http://www.youtube.com/watch?v=hfZ
8o9D1tus

DNA  RNA  Protein  Trait
Stucture of RNA
Single stranded
Sugar is ribose instead of deoxyribose
Uracil (U) replaces Thymine (T)

Messenger RNA – mRNA, contains
“code” or instructions for making a particular protein
Ribosomal RNA – rRNA (part of the ribosome), facilitates the orderly linking of amino acids into polypeptide chains
Transfer RNA – tRNA, brings amino acids from the cytoplasm to the ribosome

Transcription is the synthesis of RNA using DNA as a template: Fig. 12-14
RNA polymerase binds to DNA strand and separates it
RNA polymerase will bind to a promoter, a specific “start’ region of the DNA molecule
Nucleotides are assembled into a strand of RNA
Transcription stops when RNA polymerase reaches a specific “stop” region of the DNA molecule

https://www.youtube.com/ watch?v=rKxZrChP0P4
This video also shows translation

Only a small portion of the original RNA sequence leaves the nucleus as mRNA because portions are edited out. Fig. 12-15
Introns are the noncoding sequences in the DNA that are edited out of the pre mRNA molecule
Exons are the coding sequences of a gene that are transcribed and expressed (translated into a protein)

Fig. 12-16, 12-17
A codon is a three-nucleotide sequence in mRNA that:
• signals the starting place for translation
• specifies which amino acid will be added to a growing polypeptide chain
• signals termination of translation
Some amino acids are coded for by more than one codon

Fig. 12-18
Translation is the synthesis of a polypeptide chain, which occurs under the idrection of mRNA
• Three major steps of translation include: Initiation, Elongation, and
Termination
• Initiation - must bring together the mRNA, two ribosomal subunits, and a tRNA

Fig. 12-18
• Elongation – polypeptide assembly line
1) Codon on mRNA bonds with anticodon site on tRNA
2) The amino acid that is brought in by tRNA is added to the growing polypeptide chain
3) tRNA leaves ribosome
• Termination – stop codon is reached and the entire complex separates

http://www.youtube.com/watch?v=5bLEDd-PSTQ
(translation)
You can also go back to transcription slide to see another video on translation

From Polypeptide to Functional Protein – depends upon a precise folding of the amino acid chain into a three-dimentional conformation

Any change in the genetic material is a mutation.
Gene mutations – changes in a single gene –
Fig. 12-20
1. point mutations – changes involving only one or a few nucleotides
(substitution, insertion, deletion) that affects only one amino acid

2. frameshift mutation (a type of point mutation) – “reading frame” of the genetic message is changed because of insertion or deletion of a nucleotide, therefore the entire sequence of amino acids can change

Substitution

Insertion and Deletion

Chromosomal mutations – changes in the number of structure of chromosomes; includes – deletion, duplication, inversion, and translocation – Fig. 12-21

Genes can be switched “on” or “off” depending on the cell’s metabolic needs, (i.e. muscle cell vs. neuron, embryonic cell vs. adult cell) Fig. 12-22

Structural gene – gene that codes for a protein
Operon – a group of genes that operate together
Operator – a DNA segment between an operon’s promoter and structural genes, which controls access of RNA polymerase to structural genes

Repressor – a specific protein that binds to an operator and blocks transcription of the operon
The lac operon is turned off by repressors and turned on by the presence of lactose.

http://www.suman
asinc.com/webcont ent/animations/co ntent/lacoperon.ht
ml (lac operon animation)

Eukaryotic genes coding for enzymes of ametabolic pathway are often scatttered over different chromosomes and havew their own promoters. Fig. 12-24
1. TATA box – a repeating sequence of nucleotides that helps position RNA polymerase to the promoter site http://www.youtube.com/watch?v=7EkSBB
DQmpE TATA box animation

2. Enhancer – noncoding DNA control sequence that enhances a gene’s transcription and that is located thousands of bases away from the gene’s promoter

Differentiation – to become more specialized
Hox – genes – a series of genes that control the differentiation of cells and tissues in the embryo – Fig. 12-25