DNA UNIT GUIDED NOTES
•
Molecular Genetics
•
DNA: Deoxyribonucleic Acid
•
A double stranded helix that encodes the genetic information.
NAME______________________
DNA is shaped like a ___________________________ called a double helix.
The _____________ of the ladder are made of alternating _______________ and _____________________
The _______________ (steps) of the ladder are made of paired __________________
The _______________or sequence of the nitrogen bases determine the proteins that are made. These proteins
determine your _________________
These elements form Nucleotides which have 3 main parts:
1. Deoxyribose (a sugar)
2. Phosphate (PO4)
3. ______________________________
HISTORY OF DNA
•
Griffith finds a ________________________________
•
Griffith experimented with the _______________________ that cause pneumonia.
•
He used two forms: the S form (deadly) and the R form (not deadly).
•
A transforming material passed from dead S bacteria to live R bacteria, making them deadly.
•
Avery identified ________________________ as the transforming principle.
•
Avery isolated and purified Griffith’s transforming principle.
•
Avery performed three tests on the transforming principle.
•
•
Hershey and Chase studied viruses that infect bacteria, or bacteriophages.
1
DNA STRUCTURE
•
DNA is composed of __________________ types of nucleotides.
•
DNA is made up of a long chain of ______________________
•
Each nucleotide has three parts.
–
a phosphate group
–
a deoxyribose sugar
–
•
Watson and Crick determined the three-dimensional structure of DNA by ____________________________.
•
They realized that DNA is a double helix that is made up of a sugar-phosphate backbone on the outside with
__________________ on the inside.
•
1952
•
Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff.
•
•
Chargaff’s rules stated that A=
•
Nucleotides always pair in the same way.
•
The base-pairing rules show how nucleotides always pair up in DNA.
•
A pairs with
•
C pairs with
and C=
DNA REPLICATION
•
•
A single strand of DNA serves as a template for a new strand.
•
The rules of base pairing direct
replication.
•
DNA is replicated during the
S (synthesis) stage of the
cell cycle.
2
•
Each body cell gets a
complete set of
identical DNA.
Why do cells divide?
•
To ________________________damaged tissue
•
To _______________________
•
To ____________________ and ______________________
•
Bacteria reproduce asexually by a type of cell division called binary fission

Cell Division—Replication Process
o
o
To produce a new cell the old cell must make a complete copy of its own DNA
1. The DNA double helix will “unzip” ____________________________ the nitrogen bases
2. Enzymes will____________________ up new nucleotides that __________________ the original nitrogen bases
3. Once all nucleotides are paired up, there will be 2 DNA double helix
o
Proteins carry out the process of replication.
•
•
Enzymes and other proteins do the actual work of replication.
–
Enzymes unzip the double helix.
–
Free-floating nucleotides form hydrogen bonds with the template strand.
–
DNA polymerase enzymes bond the nucleotides together to form the double helix.
–
–
Two new molecules of DNA are formed, each with an original strand and a newly formed strand.
–


o Replication is fast and accurate.
DNA replication starts at many points in eukaryotic chromosomes
o
Cell Division—Replication Process
Review the nitrogen bases
3
A-adenine pairs only with _______________________
G-guanine pairs only with __________________________


Therefore the percentage of Adenine in a DNA strand will be equal to the percentage of Thymine and the
percentage of Guanine is equal to the percentage of Cytosine in the same strand.
Therefore determine what the new DNA strand will look like:
AGGTACATGGGACCT
TCCATGTACCCTGGA
•
o
DNA TRANSCRIPTION

o
RNA carries DNA’s instructions.
The central dogma states that information flows in one direction from DNA to RNA to proteins.






•
The central dogma includes three processes



RNA is a link between DNA and proteins
RNA differs from DNA in three major ways



o Transcription makes three types of RNA.
Messenger RNA (____________________) carries the message that will be translated to form a protein.
Ribosomal RNA (__________________) forms part of ribosomes where proteins are made.
Transfer RNA (_________________) brings amino acids from the cytoplasm to a ribosome.
o
Transcription is catalyzed by RNA polymerase
 RNA polymerase and other proteins form a transcription complex.
 The transcription complex recognizes the start of a gene and unwinds a segment of it.

 RNA polymerase bonds the nucleotides together.
 The DNA helix winds again as the gene is transcribed+

o
The transcription process is similar to replication.
Transcription and replication both involve complex enzymes and complementary base pairing.
4
•
The two processes have different end results.
•
•
o
DNA TRANSLATION
•
•
Translation converts mRNA messages into polypeptides.
•
A codon is a sequence of three nucleotides that codes for an amino acid.
•
•
three stop codons
•
one start codon, codes for methionine
•
A change in the order in which codons are read changes the resulting protein.
•
o
•
Amino acids are linked to become a protein.
An anticodon is a set of three nucleotides that is complementary to an mRNA codon.
•
o
Ribosomes consist of two subunits.
•
The large subunit has three binding sites for tRNA.
•
The small subunit binds to mRNA.
•
o
For translation to begin, tRNA binds to a start codon and signals the ribosome to assemble.
 A complementary tRNA molecule binds to the exposed codon, bringing its amino acid
close to the first amino acid.
 The ribosome helps form a polypeptide bond between the amino acids.


 A complementary tRNA molecule binds to the next exposed codon.
 Once the stop codon is reached, the ribosome releases the protein and disassembles.
o
GENE EXPRESSION
Gene expression is carefully regulated in both prokaryotic and eukaryotic cells.
•
5
•
Mutation page 5
1. Definition– _______________________
2. Mutations During Replication
•
Mutations in ________________ will cause a change in ______________________
•
A change in the protein will cause a change in _________________
•
Mutations of DNA occurs during _____________________ of DNA or ______________________
2. What causes DNA to change?
a. errors in ____________________________
b. environmental causes
i. exposure to ultraviolet radiation (sunlight)
3. These mutations cause:
a. ______________: change in the protein
b. ____________
: change in the protein
c. no effect: no change in the protein
o
•
Mutations are changes in DNA that may or may not affect phenotype.
Some mutations affect a single gene, while others affect an entire chromosome.
–
–
A mutation may occur in a noncoding region.
–
A mutation may not affect protein folding or the active site.
•
•
Mutations in sex cells can be harmful or beneficial to offspring.
•
Natural selection often removes mutant alleles from a population when they are less adaptive.
o
•
A mutation is a change in an organism’s DNA.
Many kinds of mutations can occur, especially during replication.
•
o
Chromosomal mutations affect many genes.

6

Gene duplication results from unequal crossing over.
o Translocation results from the exchange of DNA segments between nonhomologous
chromosomes
o
Mutations may or may not affect phenotype.
•
•
Some gene mutations change phenotype.
–
A mutation may cause a premature stop codon.
–
–
A mutation may change gene regulation.
o
Mutations can be caused by several factors.
•
Replication errors can cause mutations.
•
Mutagens, such as UV ray and chemicals, can cause mutations.
•
Some cancer drugs use mutagenic properties to kill cancer cells.
•
DNA sequencing: A process of determining the order of nucleotide bases in DNA.
•
PCR: Polymerase chain reaction. Used to amplify DNA so that there is a larger quantity to perform DNA
sequencing on.
•
Human Genome Project: An international project that sequenced the human genome. Completed in 2003.
•
DNA fingerprinting: An individuals unique sequence of DNA base pairs.
•
Transgenic organism: An organism whose DNA has been changed by adding DNA from another source.
•
Cloning: Reproduction of a genetically identical organism.
•
Genetically engineered plants and animals
•
Organisms whose DNA has been altered using recombinant DNA techniques.
7