Download The Fourth Macromolecule!!!

The Fourth Macromolecule!!!
1.
Objectives:
Describe the structure and function of DNA and RNA
2.
Explain how DNA replicates itself
3.
Explain the purpose of DNA replication
There are two types of nucleic acid
1. DNA
2. RNA
1. DNA: deoxyribonucleic acid
• The genetic information of a cell
• Located in the nucleus
• Works with RNA to regulate the order of
amino acids in proteins
• Made of 4 nucleotides: adenine, thymine,
cytosine, guanine
• In DNA, the central sugar is a deoxyribose
Nucleotides join together through covalent
bonds …
… And join together with another chain of nucleotides through
hydrogen bonds
• DNA consists of two chains of nucleotides
joined together in the middle by hydrogen
bonds between the nitrogenous bases.
• Adenine pairs with Thymine A ====== T
hydrogen bonds)
• Cytosine pairs with Guanine C ====== G
hydrogen bonds)
• these pairs are called “complementary
base pairs” meaning that they have shapes
Question
• Give the complementary base pairing for
the following sequence…
AGT TAA CCG
We know that to function as a genetic
material, DNA has to be able to do three
things:
1) replicate (duplicate) itself so that it can
be transmitted to future generations
2) store information
3) undergo mutations (changes) that
provide genetic variability (to account for
the variety in living things)
• Before a cell divides, DNA must replicate or make an
exact copy of itself.
• Each of the two new cells that will be produced after
cell division occurs, will receive one complete set of
DNA.
• Each strand serves as a template for the building of a
new strand
• Each original strand produces a new strand of DNA
beside itself by complementary base pairing
• The result is two new DNA double helices, identical
to each other and to the original DNA molecule (two
copies)
• DNA is
making an
exact copy
of itself
Parental (old)
DNA molecule
Daughter
(new) strand
Daughter
DNA molecule
(double helices)
Figure 10.6
• DNA replication begins at multiple sites along
the DNA called origins of replication:
1. DNA unwinds and unzips. Each strand will now
serve as a template (blueprint or mold)
2. Free nucleotides present in the nucleus are fitted
into place beside each original strand following the
complementary base pairing rule
3. These new nucleotides are joined together into a
strand by an enzyme called DNA polymerase.
4. When the process is completed the result is two
identical DNA molecules being formed.
Origin of
replication
Origin of
replication
Origin of
replication
Parental strand
Daughter strand
Bubble
Two identical daughter DNA molecules
http://www.dnatube.com/video/365/DNA-Replication
Figure 10.8
• Mistakes in base pairing rarely occur
during DNA replication
• Normally a DNA repair enzyme checks
each base pair and repairs any mistakes,
by removing the wrong base and inserting
the correct one
• A mutation is an error in DNA that
persists causing a permanent change in
the sequence of bases
• A mutation can cause a change in the
protein produced and ultimately a change
in the trait controlled by that gene.
• This may be harmless or serious (disease
causing)
• Mutations can also be caused by
exposure to toxic chemicals, ionizing
radiation, ultraviolet light (sun exposure) or
viruses.
• If the sequence of DNA bases on one
strand of the double helix is CGT-AATCGC-TTA, what will be the
complementary sequence on the other
side of the double helix?
Your Task
• Draw a diagram illustrating the process of
DNA replication.
• Include in your diagram:
– 1.
The correct structure of DNA (labeled)
– 2.
The steps involved in DNA replication
(labeled)
– 3.
Show how the free nucleotides in the
nucleus pair up with their complementary
base on each template strand of DNA
Plenary…
1. What are the three major groups of
chemicals in DNA?
2. If DNA is only composed of three types
of chemicals, why are living things so
different from each other?
3. What are the base pairs in DNA?
But…what’s so important about DNA?
• In a cell all functions are carried out by proteins:
control of cell reproduction, production of
energy, production of hormones, production of
digestive enzymes, etc.
• DNA contains genes: the blueprints for those
proteins
• Each gene is an assembly guide (think IKEA)
on how to put the protein together