Download DNA

DNA
Characteristics of DNA
1.
2.
3.
Supplies instructions for cell processes, like
how to make proteins
Can be copied each time a cell divides
It is the “blueprint of life”, every living thing
has DNA
DNA Structure


Is a nucleic acid that is double stranded
Made up of subunits called nucleotides
A nucleotide consists of 3 parts:
1.
2.
3.
Phosphate
Sugar
Nitrogen base:
adenine (A),
guanine (G),
thymine (T),
cytosine (C)
Section 12-1
Structure of DNA
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Scientific Contributions
Watson and Crick: made a model of DNA
structure in 1953

The “Double Helix” looks like a twisted
ladder



Sides of the ladder are alternating sugar and
phosphate units
Rungs are the bases held together by
hydrogen bonds
A always pairs with T and C always pairs with
G
DNA Replication

Def: Ability of DNA to make an exact copy or
a new strand of DNA from an old one
The Steps in Replication
1.
2.
3.
4.
Start with a DNA molecule
Hydrogen bonds break and the strands
separate (unzip)
Add matching nucleotides
The result: 2 identical DNA molecules
½ old strand, ½ new strand
Drawing DNA Replication:
Step 1
Drawing DNA Replication:
Steps 2 and 3
Drawing DNA Replication:
Step 4
DNA Replication:
Chromosomes

Tight coils and supercoils of DNA and protein
Section 12-2
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
Protein Synthesis
Genetics: The Science of Heredity
Genes and the Genetic Code
Gene: a segment of DNA on a chromosomes that codes for
a specific trait
Genetic Code: formed by the order of nitrogen bases along
a gene that specifies what type of protein will be produced
Genetics: The Science of Heredity
How cells make proteins
A cell uses the coded information from a segment of DNA
(gene) to make a specific protein
Why make proteins?
Proteins determine your traits, hair color, eye color, tongue
rolling ability, etc.
Things that are not traits: athletic ability
Genetics: The Science of Heredity
What Protein Synthesis involves:
DNA found in the nucleus
Ribosome: where the proteins are made
RNA (see below)
Amino acids: these are the building blocks of
proteins
Genetics: The Science of Heredity
RNA
Similar to DNA
Structure of RNA:
Sugar is different
Single-stranded
Uracil replaces thymine
Still has cytosine (C), guanine (G), and adenine (A)
Genetics: The Science of Heredity
DNA vs RNA
Genetics: The Science of Heredity
2 Types of RNA
mRNA: messenger RNA
Copies the coded message from the DNA in the nucleus
and carries the message to the ribosome in the
cytoplasm
tRNA: transfer RNA
Picks up and transfers amino acids in the cytoplasm to the
ribosome and adds them to the growing proteins
Genetics: The Science of Heredity - The DNA Connection
How Cells Make Proteins
During protein synthesis, the cell uses information from a
gene on a chromosome to produce a specific protein.
Genetics: The Science of Heredity - The DNA Connection
Mutations
Mutations can cause a cell to produce an incorrect protein
during protein synthesis. As a result, the organism’s trait, or
phenotype, may be different from what it normally would
have been.
Genetics: The Science of Heredity
So, what’s the big deal?
Mutations happen all the time
most of the time they are fixed by our bodies
Genetics: The Science of Heredity
If they are not fixed, 3 things could happen:
1. Absolutely nothing:
occurs most of the time
2. A small change:
like having 2 different color eyes
a change that does not effect the way you live
Genetics: The Science of Heredity
3. A BIG change: (can be good or bad)
like getting a disease or being able to blend in to your
environment better
has a big effect on how you live