Download Chapter 12 DNA and RNA

Chapter 12
DNA and RNA
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Understanding Genetics
I’d like to better
understand
genetics…
Well, then…we need
to understand the
chemical makeup
of the gene
Understanding Genetics
Sweet! Genes
are made of
DNA…
Yeah, DNA can store
genetic information,
and transmit it to
the next
generation!
Understanding Genetics
Let’s study
this DNA and
figure out how
it carries
information
Far out, maybe we’ll
find out how it
decides traits and
replicates itself,
too!
Understanding Genetics
Replicates?
What on earth
does that
mean?
Dude – DNA can make
a copy of itself –
that’s called
replication!
History and Structure
• In 1953, two scientists, James
Watson & Francis Crick, built
model of DNA out of tin & wire
– Looked like a twisted ladder
– Called the shape a Double Helix
(2 twisting strands)
Structure
• Sides of ladder are sugar &
phosphate groups
• Rungs of ladder are nitrogen
bases joined together by H
bonds
DNA
Structure
Structure
• DNA = deoxyribonucleic acid
– Long molecules of nucleotides
linked together like a chain
Structure
• Each nucleotide is
made of 3 parts:
– Phosphate Group
– 5-Carbon Sugar
(deoxyribose)
– Nitrogen Base
Structure
• 5-C sugar & phosphate group
always the same for each
nucleotide in DNA
– Form sides of ladder
Structure
• There are 4 different
nitrogen bases:
– Adenine
– Guanine
– Thymine
– Cytosine
Structure
• Adenine & Guanine classified
as Purines
– Because they are larger
molecules with double rings of
Carbon & Nitrogen
Structure
• Cytosine & Thymine classified
as Pyrimidines
– Because they are made of a
single ring of Carbon &
Nitrogen
Note the single and double
rings. What else do you notice?
BASE PAIRING
• Since A always pairs with T (A-T)
and C always pairs with G (C-G),
DNA strands considered
complementary to each other
– They match
– Think of the color wheel!
• Are the same
in every
organism
• The
nucleotides
are in a
DIFFERENT
order for each
organism
• DNA is found in the nucleus of cells.
- contain both DNA and
protein tightly packed together to form a
substance called chromatin.
• An area of coded DNA on a given
chromosome that gives a certain trait.
• Traits such as height, eye and hair color is
coded in your genes.
• To analyze chromosomes, cell biologists
PHOTOGRAPH cells in MITOSIS.
• Next, they cut out the chromosomes
and group them in pairs.
• This is called a KARYOTYPE
• Replication is the
process of copying
DNA
• During replication
each strand serves as
a pattern to make a
new DNA molecule
• Enzymes (DNA
polymerase) break
hydrogen bonds between
nitrogen bases
• Molecule unzips
• Unzipped molecule base
pairs with free
nucleotides
• Two copies of
the organism’s
genetic
information
that can be
passed during
mitosis or
meiosis
Replication Summary
• In DNA replication, enzymes work to
unzip & separate the double helix.
• Complementary bases are added to the
open strands.
• Each new double helix is made of one old
DNA strand & one new strand.
http://nobelprize.org/educational_games/medicine/dna_double_helix/
12-3: Protein Synthesis
• RNA is…
• Single stranded
• Contains ribose
• Contains the base uracil
instead of thymine
• Three types:
– Messenger (mRNA)
• Carry copies of instructions for assembling
amino acids into proteins.
– Ribosomal (rRNA)
• Along with proteins, rRNA makes up ribosomes
where proteins are assembled.
– Transfer (tRNA)
• Transfers amino acids to the ribosome as it is
specified by coded messages in mRNA.
• Process of making an RNA copy of a DNA
strand
• Results in the formation of a singlestranded RNA molecule
• mRNA carries the information for making
proteins to the ribosomes
•Since directions for making
proteins are in the nucleus
the mRNA has to take the
info to the cytoplasm where
the ribosomes can make
proteins!
• DNA molecule unzips
• Free RNA nucleotides pair
with complementary DNA
strands
• mRNA breaks away and the
DNA strand rejoins
• Proteins are made by joining amino acids
into long chains called polypeptides.
• Each polypeptide contains any combination
of the 20 amino acids.
– The properties of proteins are determined by
the order of each of these different amino
acids.
• Each set of three nitrogen bases
representing an amino acid is known as a
codon—triplet code
• 64 combinations possible; 61 code for amino
acids and 3 code for stop signals
• The process of converting information in
a sequence of nitrogen bases in mRNA
into a sequence of amino acids that make
up a protein
• Decoding the message
• tRNA brings
amino acids to
the ribosomes
so they can be
assembled into
proteins
So you may be thinking….
• Why do we need proteins?
• Proteins:
– Most are enzymes that code for….
– Production of a pigment to control the
color of a flower
– Production of red blood cell surface
antigen (determines blood type)
– Regulate the rate and pattern of growth
throughout an organism (controls size and
shape)
Mutations
• Sometimes cells make mistakes when
copying their own DNA…these mistakes
are called MUTATIONS!
– Changes in the genetic material of the cell.
• Many mutations are not harmful, some
even increase genetic variation in a
species!
• Mutations that are harmful can cause
genetic disorders and sometimes cancer.
Types of Mutations
• Single base-pair substitution
• Deletion or insertion of one or more
base pairs
• Major alteration in the structure of a
chromosome.
• May or may not bring about a change in
a phenotype. WHY?
Mutations-classified by location
• Cells
– Somatic: occur in any cell in the body except gametes
(Localized cell death, altered cellular function, or tumors)
– Sex-cells: occur in gametes (creates genetic diversity
and/or disease)
• Chromosome…in all of the cells!
– Autosomal: occur within genes located on the autosomes
(chromosome pairs 1-22)
– X-linked: occur on the X chromosome
Mutations: classified by type of change
POINT (changes base pair)
• If there is not a change in AA, then
it is a silent mutation.
• Missense mutation: Change of
one nucleotide, may change the
AA that the codon called for.
• Nonsense mutation: Triplet will
be changed into a stop codon,
resulting in a termination of
translation.
FRAMESHIFT
• Addition or deletion of a
single letter, which causes all
of the rest of the letters to be
“MOVED” by one space.