dna (deoxyribonucleic acid). transformation of bacteria
TRANSCRIPT
What carries hereditary information?
By the 1940s, scientists knew that chromosomes carried genes.
They also knew that chromosomes were made of DNA and protein.
They did NOT know which of these molecules actually carried the genes.
Since protein has 20 types of amino acids that make it up, and DNA only has 4 types of building blocks, it was a logical conclusion.
Most Scientists thought protein carried genes
Avery’s Experiment1. Avery repeated Griffith’s experiments with an additional step to see what type of molecule caused transformation.
3. When Avery added enzymes that destroy
DNA, no transformation occurred.
2. Avery used enzymes to destroy the sugars and transformation still occurred—Sugar did not cause transformation. Avery used enzymes to destroy lipids, RNA, and protein one by one. Every time transformation still occurred—none of these had anything to do with the transformation.
So…he knew that DNA carried hereditary
information!
The experiment involved viruses to see if DNA or protein was injected into the bacteria in order to make new viruses.
One group of viruses was infected with radioactive protein and another group with radioactive DNA.
Then the viruses attack the bacteria.
Radioactive DNA shows up in the bacteria, but no radioactive protein.
Hershey-Chase Experiment
Chargaff’s Rules
The amount of adenine (A) equals the amount of thymine (T).
The amount of cytosine (C) equals the amount of guanine (G).
Rosalind Franklin Took X-ray
pictures of DNA. The photos
revealed the basic helix, spiral shape of DNA.
Maurice Wilkins Worked with
Rosalind Franklin. Took her x-ray
photos and information to Watson and Crick
Watson and Crick
Used Franklin’s pictures to build a series of large models.
Stated that DNA is a double-stranded molecule in the shape of a double helix, or twisted ladder.
Won the Nobel Prize for their work in 1962.
Basic DNA Structure
S
P
A
CS
P
S
P
T
G S
P
S
P
A
T S
P
A nucleotide is the monomer of DNA A nucleotide is made of
– a sugar called deoxyribose– a phosphate– and a base (ATCG)
The two strands of DNA are held together by hydrogen bonds
DNA Replication
1. The DNA molecule
separates into its 2 strands by
breaking the hydrogen
bonds.
3. An enzyme called DNA polymerase adds new complementary nucleotides to each original strand.
2. Each old strand becomes a template for a new strand.
DNA makes a copy of itself.
Add New NucleotidesFill in the correct nucleotides that will be added.
T
G S
S
P
P
S
P
A
S
P
A
CS
P
S
P
T
T S
P
G S
P
S
P
A
S
P
A
CS
P
S
P
T
Questions Are the two copies of DNA the
same?
Why would it be important for the two copies of DNA to be the same?
What is a Gene? A gene is a
code found in DNA
Genes code for proteins that give people their traits.
How does DNA code for so many traits with only 4 bases?
Can you spell 20 words with the letters A, T, C and G?
Each combination of bases codes for a different amino acid.
Putting the 20 amino acids in different orders makes different proteins.
RNA Single-stranded nucleic acid Made of nucleotides Has ribose instead of deoxyribose Has uracil instead of thymine
Transcription
DNA’s code is transcribed onto mRNA. mRNA has complementary bases to the DNA. Each codon is made of three bases.
Translation
Translation begins at the start codon (AUG) of mRNA
Then each codon codes for an amino acid in a protein that is brought in by a tRNA.
tRNA has complementary bases to mRNA Translation is terminated by stop codon.
Mutations Mutation-alteration in
DNA Mutagens-physical and
chemical agents that mutate DNA
Deletion-mutation caused by deleting DNA that should be there
Insertion-mutation caused by inserting DNA that should not be there
Substitution-mutation caused by substituting DNA
Inversion-DNA is inverted or flipped
Gene Regulation Genes are not expressed all the time. Some genes are usually on, but can
be turned off by repressors when they are not needed.
Some genes are usually off, but they can be turned on by enhancers when they are needed.