Transcript My DNA Notes

The Components and
Structure of DNA
• Structure:
Deoxyribonucleic acid
• Found in all living things
Double Helix
• DNA strands were
twisted around each
other like the coils of
a spring, a shape
known as a double
helix.
• A double helix looks
like a twisted ladder
or a spiral staircase.
How could DNA, or any other molecule, do the
three critical things that genes were known for? :
1. Genes had to carry information from one
generation to the next.
2. Put the information to work by determining
the heritable characteristics of organisms.
3. Be easily copied, because all of the cell’s
genetic information is replicated every time
a cell divides.
Nucleotides
• DNA is a long
molecule made up of
units called
nucleotides.
Each nucleotide is
made up of three
basic components:
1. 5-Carbon sugar
called deoxyribose
2. Phosphate group
3. Nitrogenous base
Bonds in DNA
1. Nucleotides are held
together by
covalent bonds
S
B
P
Covalent bonds
• 2. Hydrogen
Bonds: 2 bases
make up the
“rungs” of the
double helix and
this is the bond they
are held together
by.
4 Kinds of Nitrogenous Bases
• Purines: made of 2 carbon
rings
• Adenine (A) & Guanine (G)
• Pyrimidines: made of 1
carbon ring
• Cytosine ( C) & Thymine
(T)
Base Pairing Rules
• Adenine only bonds to Thymine
(A) = (T)
• Guanine only bonds with Cytosine
(G) = (C)
Functions
• The function of
DNA is to store and
transmit genetic
information that
tells cells which
proteins to make
and when to make
them.
Matching
• 2 sides of DNA are
complementary to
one another.
• If you know one
side of the helix
you can figure out
the other side.
• TACGTCGTA
• ATGCAGCAT
Replicate DNA
1. DNA “unzips” at
one end by
breaking up the
hydrogen bonds
between bases
2. Free floating
nucleotides pair
with the open
bases on each
side of the double
helix.
3. Continues until DNA
double helix
“unzips” and 2
double helixes are
made. Each double
helix has one new
strand and one old
strand. Both are
identical to each
other and to the
original.
RNA
• Ribonucleic acid
• Single strand no double helix
• Made of repeating monomers
called nucleotides
Nucleotides
Each nucleotide
consists of 3 parts:
1. 5-Carbon sugar
called ribose
2. Phosphate group
3. Nitrogenous base
4 Types of Bases
• Purines: Adenine (A) &
Guanine (G)
• Pryimidines: Cytosine ( C)
& Uracil (U)
Base Pairing Rules
In RNA
• Adenine only bonds to Uracil
(A) = (U)
• Guanine only bonds with Cytosine
(G) = (C)
3 Types of RNA
Messenger RNA (mRNA)
• 3 nucleotide
bases on RNA
are called a
codon
• Holds genetic
info from a DNA
strand and
translated into
protein.
3 Types of RNA
Transfer RNA (tRNA)
• Each tRNA
bonds only to
specific amino
acids
• Has location
called the
anticodon, a 3
nucleotide base
sequence.
3 Types of RNA
Ribosomal RNA (rRNA)
• Makes up a ribosome
• “reads” the mRNA strand
• For a cell to make a protein, the
information from a gene is copied,
base by base, from DNA into new
strands of mRNA. The mRNA
travels out of the nucleus into the
cytoplasm, to ribosomes. mRNA
directs assembly of amino acids
that fold into completed protein
molecules.
Genetic Code
• Proteins are made of amino acids
• 20 known amino acids
• Sequence of nucleotides (bases) on
DNA determines what amino acids are
put into proteins.
How many nucleotides (bases) are
used to code for each amino acid? 3
• Read 1 base=at most only 4 combinations
• Read 2 bases=at most only 16 combinations
• Read 3 base=at most only 64 combinations
• 3 bases must be read at one time to code for
1 amino acid
• A 3 base sequence found on an mRNA is
called a codon
• 60 combinations of 3 bases code just for
amino acids
• 1 combination codes for a start as well
as an amino acid. (AUG-Methionine).
Methionine is the only amino acid
specified by just 1 codon, AUG.
• 3 combinations code for a stop codon.
The stop codons are UAA, UAG, and
UGA. They encode NO amino acid.
The ribosome passes ad falls off the
mRNA .
Transcription
• Process where
part of DNA
double helix (a
gene) is “read”
and a strand of
mRNA is
created.
Steps
1. DNA double helix “unzips” down
the center between the bases at a
certain location of the helix.
2. One side of the double helix is
“read” starting at a certain base
and “read” to a certain base
(gene)
3. A complementary
strand of mRNA is
created.
4. DNA double helix
“zips” back up.
5. Strand of mRNA
leaves the nucleus.
Translation
• Process where a
mRNA strand is
“read” and a
protein is
produced.
Steps
1. A ribosome (which is made of
rRNA) attaches to the strand of
mRNA at a certain spot (AUGstart codon)
2. Ribosome reads the first 3 bases
(called a codon) on the mRNA
strand.
3. A tRNA that has an anticodon, that
is a complement to the codon being
read, attaches to the mRNA.
Remember that tRNA’s have an
amino acid attached to them
Ex. Codon(on mRNA)- AUG
Anticodon(on tRNA)= UAC
4. The tRNA leaves the rRNA but
leaves the amino acid
5. Ribosomes reads the next codon
on mRNA.
6. Repeat steps 3-5 until the certain
codon is read called the stop
codon.
7. Ribosome lets go of the mRNA
strand.
8. All the amino acids that were
brought by the tRNA are linked
together producing a protein.
9. (Practicing)
DNA mRNA strand  Protein
Mutations
•
•
•
•
Most are minor
Many are
harmful
Some are lethal
Very few are
helpful
Types of Mutations
I.
Point Mutationschanges involving one
nitrogen base
A. Frameshift
Mutations- that
Addition or Deletion of
a nitrogen base,
causing the gene
sequence to read out of
sequence
Types of Mutations
1.
InsertionEx. ACG/TAG/GTA
ACG/TTA/GGT/A
2.
Deletions: A piece of
chromosome breaks
off and is lost
Ex. ACG/TAC/GTA
ACG/TACG/TA
B. Base SubstitutionEx. ACG/TAC/GTA
ACG/TAA/GTA
Types of Mutations
II. Chromosome MutationsInvolve segments of
DNA
A. Inversion: Reinsertion
of a sequence
backwards
EX.
AGCTAGCTA 
AGGATCCTA
Types of Mutations
B. Translocation- A piece
of a different
chromosome is
added to another
EX.
AGCTAGCTA 
AGCTAGCTATCCAG