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Notes beginning 3/24/17
DNA & Protein Synthesis
Before the 1940’s scientists didn’t know what material caused inheritance.
They suspected it was either DNA or proteins.
A series of experiments proved that DNA was the genetic material responsible for inheritance.
In 1952, Alfred Hershey and Martha Chase did an experiment using a virus that infects E. coli bacteria.
The experiment proved that DNA and not protein is the factor that influences inheritance.
Erwin Chargaff discovered the base pairing rules and ratios for different species.
Adenine pairs with Thymine
Cytosine pairs with Guanine.
Rosalind Franklin & Maurice Wilkins had taken the 1st pictures of DNA using X-ray crystallization
This proved that DNA had a helical shape.
The Nobel Prize in Medicine 1962
Francis Harry Compton Crick
James Dewey Watson
(Died of cancer 1958)
Maurice Hugh Frederick Wilkins
Wilkins has become a historical footnote and Watson & Crick are remembered as the Fathers of DNA
(A, T, G, C)
DNA - double helix
The genetic code is a sequence of DNA nucleotides in the nucleus of cells.
DNA is a double-stranded molecule.
The strands are connected by complementary nucleotide pairs (A-T & C-G) like rungs on a ladder.
The ladder twists to form a double helix.
During S stage in interphase, DNA replicates itself.
DNA replication is a semi-conservative process.
Semi-conservative means that you conserve part of the original structure in the new one.
You end up with 2 identical strands of DNA.
Replication: Copy this down
Eat my DNA activity
Gene - a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color, etc.)
A gene is a stretch of DNA.
A mistake in DNA replication is called a mutation.
Many enzymes are involved in finding and repairing mistakes.
What causes mutations?
Can occur spontaneously
Can be caused by a mutagen
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.
Some mutations can:
Have little to no effect
Be beneficial (produce organisms that are better suited to their environments)
Be deleterious (harmful)
Types of mutations
Point Mutations : causes the replacement of a single base nucleotide with another nucleotide
Missense- code for a different amino acid
(AUU= isoleucine, AUC= threonine)
Nonsense- code for a stop, which can shorten the protein
Silent- code for the same amino acid (AUU and AUC both code for isoleucine)
Example: Sickle Cell Anemia
Frame Shift Mutations: the number of nucleotides inserted or deleted is not a multiple of three, so that every codon beyond the point of insertion or deletion is read incorrectly during translation.
Ex.: Crohn’s disease
Chromosomal Inversions: an entire section of DNA is reversed.
a bleeding disorder
A complex system of enzymes, active in the G2 stage of interphase, serves as a back up to repair damaged DNA before it is dispersed into new cells during mitosis.
(A, U , G, C )
Function: obtain information from DNA & synthesizes proteins
3 differences from DNA
Single strand instead of double strand
Ribose instead of deoxyribose
Uracil instead of thymine
3 types of RNA
Messenger RNA (mRNA)- copies information from DNA for protein synthesis
Codon- 3 base pairs that
code for a single amino
2. Transfer RNA (tRNA)- collects amino acids for protein synthesis
Anticodon-a sequence of 3 bases that are complementary base pairs to a codon in the mRNA
3.Ribosomal RNA (rRNA)- combines with proteins to form ribosomes
Amino acids- the building blocks of protein
At least one kind of tRNA is present for each of the 20 amino acids used in protein synthesis.
Transcription - mRNA is made from DNA & goes to the ribosome
Translation - Proteins are made from the message on the mRNA
In order for cells to make proteins, the DNA code must be transcribed (copied) to mRNA.
The mRNA carries the code from the nucleus to the ribosomes.
Make A Protein
ATG AAA AAC AAG GTA TAG
UAC UUU UUG UUC CAU AUC
At the ribosome, amino acids (AA) are linked together to form specific proteins.
The amino acid sequence is directed by the mRNA molecule.
AUG AAA AAC AAG GUA UAG
Amino Acid sequence
DNA TAC AAT CGC TGT TGC TAG
mRNA UAC GCU CCC UUA GUG AUC
DNA ATG GGC TAA TTT CGC AGG
tRNA AUG UGC AUA CAU GUC UUU
Human Genome Project
The Human Genome Project is a collaborative effort of scientists around the world to map the entire gene sequence of organisms.
This information will be useful in detection, prevention, and treatment of many genetic diseases.
DNA technologies allow scientists to identify, study, and modify genes.
Forensic identification is an example of the application of DNA technology.
Gene therapy is a technique for correcting defective genes responsible for disease development.
Possible cures for:
and many other diseases is possible.
The human manipulation of the genetic material of a cell.
Recombinant DNA- Genetically engineered DNA prepared by splicing genes from one species into the cells of a different species. Such DNA becomes part of the host's genetic makeup and is replicated.
Genetic engineering techniques are used in a variety of industries, in agriculture, in basic research, and in medicine.
This genetically engineered cow resists infections of the udders and can help to increase dairy production.
There is great potential for the development of useful products through genetic engineering
EX., human growth hormone, insulin, and pest- and disease-resistant fruits and vegetables
Seedless watermelons are genetically engineered
We can now grow new body parts and soon donating blood will be a thing of the past, but will we go too far?
Photo of a mouse growing a "human ear"
inserted or deleted is not a multiple of three, so that every codon beyond the point of insertion or deletion is read incorrectly during translation.