1. DNA and Genes
Biology: Chapter 11

2. DNA Deoxyribonucleic Acid (DNA)
The genetic material
Contains the “blueprint” for an organism
Instructions for an organism’s traits
Nucleic Acid-polymer (chain) of nucleotides
Very long molecule
A single strand is ~5 feet long
If all uncoiled, your DNA would reach from the Earth to the Sun
600+ times!
DNA is too large to leave the nucleus through the pores

3. DNA, Genes, and Chromosomes
DNA=hereditary material
Gene=segment of DNA that codes for a specific protein
Chromosome=tightly wound strand of DNA and proteins

4. Structure of Nucleotides
A nucleotide is a subunit of DNA (a monomer)
3 parts:
A Sugar (deoxyribose)
A phosphate group
A nitrogenous base (Adenine (A), Thymine (T), Cytosine (C), or Guanine (G)
All organisms have these same 4 bases
Bases come in 2 forms
Purines: Adenine and Guanine
Pure as Gold
Pyrimidines: Cytosine, Uracil (to be discussed later) and Thymine
Py Cut

5. Structure of DNA DNA is a string of nucleotides
The structure was discovered by Rosalind Franklin using X-Ray technology

6. Watson and Crick James Watson and Francis Crick (1953)
“Used” Frankin’s work to come up with the 3-D structure of DNA
DNA resembles a twisted ladder or twisted zipper
Called a Double Helix
Nucleotides are held together by hydrogen bonds

7. Nucleotide Sequences
The sequence of nucleotides determines the make-up of the organism
The sequence of nucleotides on a strand of DNA is called a gene
A gene is a segment of DNA that is a code for a specific protein

8. DNA Replication DNA must constantly replicate Simplified Process
New copy is used during cell division and production of sperm and egg (mitosis and meiosis-to be discussed later)
Simplified Process
An enzyme called DNA Helicase breaks the hydrogen bonds between nucleotides
This “unzips” the strand
Another enzyme called DNA Polymerase adds a complementary nucleotide

10. Complementary Base Pairing
A bonds to T (apple tree)
C bonds to G (car garage)
Practice: What would be the complementary strand for the following?
A T G C T G
T A C G A C

11. RNA Also a nucleic acid (polymer of nucleotides) Very similar to DNA
3 parts:
A sugar (ribose)
A phosphate group
A nitrogenous base (Adenine (A), Cytosine (C), Guanine (G), and Uracil (U)
Uracil replaces Thymine
Bonds to Adenine
3 types of RNA
Messenger RNA (mRNA)-Brings instructions from DNA to cytoplasm (ribosome)
Ribosomal RNA (rRNA)-Binds to mRNA and assembles amino acids in correct order
Transfer RNA (tRNA)-Carries amino acids to the ribosome

12. Transcription DNA double helix unwinds
RNA nucleotides (A, U, G, C) bond to the complementary base
mRNA strand breaks away
mRNA leaves the nucleus and travels to the cytoplasm, where it binds to a ribosome
rRNA within the ribosome binds to the mRNA and “reads” the code

13. Amino Acids
“The language of proteins uses an alphabet of amino acids.”
There are 20 common amino acids
The sequence of nucleotides determines the sequence of amino acids
3 bases code for one amino acid
This group of 3 bases is called a codon
Example: U U U = phenylalanine
Several codons code for the same amino acid
Example UUU and UUC both code for phenylalanine
Some codons are not codes for amino acids, but instructions to start or stop transcription.
AUG=Start codon (Methionine)
UGA, UAA, and UAG=Stop codons

15. Translation
Translating mRNA into a sequence of amino acids to form a protein
Amino acids dissolved in the cytoplasm are brought to the ribosome by tRNA
tRNA contains a sequence of 3 amino acids called an anticodon
The anticodon is complementary to a codon.
Example: AUG is a start codon and codes for the amino acid Methionine
Methionine will be attached to a tRNA molecule that has the anticodon UAC
As the amino acids attach to the mRNA strand, the tRNA releases and returns to the cytoplasm to pick up another amino acid
Peptide bonds are formed between the amino acids, forming a protein

16. Protein structure
The sequence of amino acids determines the protein’s shape
Proteins always form in the same 3-D shape
These proteins become enzymes and cell structures.
Central Dogma of Biology
DNARNAProteins
This occurs in all organisms
It also explain how you get your traits
You get some DNA from mom, some from dad, and this DNA determines the proteins and, therefore, all of the traits you have.

17. When things go wrong Mutation-Change in DNA sequence
Can be caused by many different things
Errors in DNA replication or transcription
Errors in cell division
External factors (mutagens)
Radiation (sun or tanning)
Smoking
Alcohol
Asbestos
Many more

18. Results of Mutations Most mutation are bad Some mutations are neutral
Can result in cell division going out of control
Leads to a mass of cells, called a tumor
This is how cancer happens.
Some mutations are neutral
Minor change, or the cell catches it and fixes or destroys it before
In rare cases, mutations are beneficial
Give the organism something it did not previously have
These are what natural selection acts on.

19. Point Mutations Change in a single base pair in DNA
Alters the amino acid, and therefore the entire 3-D structure of the protein

20. Frameshift Mutations Shifts the reading of codons by one base
Unlike point mutations, all amino acids after the mutation are altered, and this drastically changes the protein shape.

21. Chromosomal Mutations
Change to the structure of a chromosome
Part of the chromosome may break off, or fold incorrectly

22. Repairing DNA Mutation sometimes occur and are able to be fixed
Certain enzymes are able to “proofread” DNA to ensure that all is well
Can replace incorrect nucleotides, or instruct the cell to destroy the DNA containing the errors
This process is not perfect, but usually works well
Best course of action is avoiding mutagens as much as possible.