Download DNA and RNA - Mrs-Lamberts-Biology

DNA, RNA
Genes
• A segment of a
chromosome that
codes for a protein.
– Genes are composed
of DNA
Three Properties of Genes:
• They carry information from one
generation to the next.
• They determine the inherited
characteristics of the organism.
• They are easily copied because genetic
information must be copied (replicated)
every time a cell divides.
The Structure of DNA:
• DNA is a long molecule composed of
nucleotide units.
• A nucleotide unit contains:
– Deoxyribose sugar
– Phosphate group
– One of four nitrogen bases:
•
•
•
•
Adenine
Guanine
Cytosine
Thymine
The Structure of DNA is a Double
Helix
• This was determined by Watson and Crick.
• Backbone of helix – sugar and phosphate
molecules.
• Rungs of ladder – nitrogenous bases.
• The strands are held together by hydrogen
bonds.
Chargaff’s Rule for Base Pairs:
• Adenine pairs with
thymine.
• Cytosine pairs with
guanine.
• Adenines = Thymines
• Cytosines = Guanines
Chromosomes in Prokaryotic Cells:
• Prokaryotic cells have
no nucleus.
• They have one ring of
DNA or RNA in the
cytoplasm.
Chromosomes in Eukaryotic Cells:
• Eukaryotic cells have 1,000 times as much DNA
as prokaryotes.
• It is packed tightly in the nucleus of the cell.
• DNA is a long molecule – the nucleus of a
human cell contains 1 meter (3 feet) of DNA.
• Chromosomes are composed of DNA wrapped
tightly around proteins called histones.
DNA Replication
• DNA must be copied before the cell can
divide.
• The DNA molecule separates – each
strand acts as a template for a new strand.
• This process results in two DNA
molecules.
• Each molecule has one original strand and
one new strand.
How is RNA different from DNA?
• DNA
– Carries the recipe for
the protein.
– Double stranded.
– Located in the
nucleus.
– Contains the sugar
deoxyribose.
– Contains the nitrogen
bases cytosine,
guanine, adenine and
thymine.
• RNA
– Makes the protein
from the recipe.
– Single stranded.
– Located in the
cytoplasm.
– Contains the sugar
ribose.
– Contains the nitrogen
bases cytosine,
guanine, adenine,
uracil.
How much DNA do we have in our
bodies?
• If all the DNA in your
body was tied
together, it would
stretch to the sun and
back 600 times!
Three Types of RNA
• mRNA – messenger RNA
– A gene is a recipe for a protein
– mRNA copies the recipe for the protein.
– It carries a copy of these instructions from the
nucleus to the cytoplasm.
• rRNA – ribosomal
RNA
– Makes up the
ribosomes.
• tRNA – transfer RNA
– Transfers amino acids
that are coded for by
the mRNA recipe from
the cytoplasm to the
ribosomes.
Protein Synthesis – Two Steps
• Transcription
– The recipe is written (in the nucleus).
• Translation
– The recipe is translated into the language of
proteins (amino acids).
Transcription
• To transcribe means “to write”.
• DNA strands separate.
• One strand serves as a template and is
copied by mRNA.
• The DNA recipe is written in 3 base
segments called triplets.
• One triplet codes for one amino acid.
• mRNA writes the recipe for a protein in its
own language.
• In the language of RNA, C pairs with G,
A pairs with U.
• This process takes place in the nucleus.
• Proteins are composed of amino acids.
• The language of mRNA instructions is
called the genetic code.
• Each word of the coded message is 3
bases long.
• This 3 base segment is called a codon.
• Each codon codes for one amino acid (20
amino acids).
Practice
• DNA triplets:
– GGG – CCC – CGC – CTT – AGG – TAT
• What would the mRNA codons be for
these triplets?
• Which amino acids would be specified for
by these codons?
Translation
• To translate means to “change to another
language”.
• The language of proteins is amino acids.
• mRNA attaches to the ribosomes with the
recipe for the protein.
• The tRNA molecule with the anticodon to
the mRNA codon brings the amino acid
called for by the recipe to the ribosomes.
• Amino acids are attached in a polypeptide
chain until the recipe for the protein is
complete.
• Translation takes place in the cytoplasm.
Practice
• Write the anticodons to the following
codons:
• CGC – GGA – AAU – UAU – ACA - GAU
Why are proteins important?
• All enzymes are proteins.
• Every chemical reaction in the body
requires an enzyme to make it go.
• Enzymes make some reactions go 1
million times faster than they would go
without the enzyme.
• Proteins regulate the rate of growth of an
organism.
• Most structures in the body are made of
proteins.
–
–
–
–
Muscles
Hair
Organs
Skin
• Proteins regulate the pattern of growth of an
organism.
• Proteins are the key to almost everything living
cells do.
Mutations
• A change in a gene or chromosome.
• Some mutations result in no change in the
organism.
• A few mutations cause favorable changes
in an organism.
• In humans, mutations usually cause harm.
• Cystic fibrosis, sickle cell anemia, Down’s
syndrome.
Gene Mutations
• Point mutations –
occur at a single point
in the DNA sequence.
• Some point mutations
simply substitute one
nucleotide for
another.
• Frameshift mutation – results in a much
bigger change because a nucleotide is
inserted or deleted.
• Every amino acid that follows the point of
insertion or deletion is affected.
Frameshift Mutations
Chromosomal Mutations
• Involve changes in
the number or
structure of
chromosomes.
Human Genome Project
• The complete recipe list for all of the
proteins needed to make a human.
• Our DNA contains more than a billion base
pairs.
• The genome was mapped in 2000.
• We were found to have about 20,000
genes that code for proteins.
• Worms have 19,098!
• Fruit flies have 13,602!
• Yeast has 6,023!
• Less than 2% of the genome actually
codes for proteins.
• 97% of the genome has no known function
(junk DNA).