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DNA: Deoxyribonucleic Acid
• DNA is the genetic material
for life
•Stores and passes on genetic
information from one
generation to another
•DNA is the instructions for
making proteins
•Protein synthesis~ making of
proteins
Names for DNA
• DNA (Deoxyribonucleic Acid):
genetic information in all organisms
• Chromosomes: Condensed DNA
• Chromatin: Uncondensed DNA coiled
around histone proteins
• Genome: All of a cell’s DNA
DNA Structure
•The DNA structure is
shaped like a spiral
staircase, or twisted
ladder called a double
helix
DNA History
• The Model of DNA was inspired by
several scientists:
– Rosalind Franklin and Maurice Wilkins:
made an X-ray of DNA that showed that
DNA was shaped like a twisted ladder
– Watson and Crick used Franklin’s X-ray
to develop the model of DNA we know
today; coined the term DOUBLE HELIX
• Double Helix- two nucleotide chains wrapped
around each other
Rosalind Franklin
Watson and Crick
Nucleotides:
DNA is a nucleic acid polymer made up
of nucleotide monomers
•Each nucleotide is
made up of:
•a sugar phosphate
backbone
• nitrogen bases
held together by
hydrogen bonds
Structure of
nucleotides
DNA Structure
•Sugar/Phosphates: The side parts of the
ladder are made of two chains of alternating
sugar (deoxyribose) and phosphate backbone
•Nitrogen bases (N-bases): The steps of
the ladder are nitrogen base pairs. These
nitrogen base pairs follow pairing rules: A-T
and C-G
•Hydrogen bonds (H-bonds): Each pair of
N-bases are held together by hydrogen bonds
in order to complete the steps of the ladder
Nitrogen Bases:
N-bases
1. Two different types of N-bases:
1. 1) Purines (A and G)- 2 rings
2. 2) Pyrimidines (C and T) - 1 ring
1.
2.
3.
4.
Adenine = A
Guanine = G
Cytosine = C
Thymine = T
They are represented by their capital
letter!
Structure of Nucleotides
DNA Structure:
Base Pairing
Base Pairing Rules: There is only
one way the nitrogen bases can
form: Purine with Pyrimidine
• Adenine pairs with Thymine (A-T)
• Guanine pairs with Cytosine (C-G)
WHY?
Pyrimidines and Purines
• Purine + Purine =
too wide
• Pyrimidine + Pyrimidine =
too narrow
DNA STRUCTURE
QUESTION ?
Can C join with A and G join with T?
Yes
No
CORRECT
MOVE ON
SORRY
REVIEW MORE
DNA STRUCTURE:
Genes
•Your genes are coded in your DNA
•A gene is represented by several base
pairs (ex eye color, hair color, height)
Below is an example of a genetic code
that may be found in your body:
ACTCATGGTCATG
TGAGTACCAGTAC
* Notice how the two strands of DNA
are complementary (A-T and C-G)
DNA STRUCTURE
•The combinations of the nitrogen
bases serve as the code that produces
the genes for a particular gene.
•Because there can be so many
different combinations of the bases,
the code can be limitless.
•This accounts for the uniqueness
among organisms
DNA STRUCTURE
EXAMPLE:
ATCGTCAGG May be for hair color
but
ATCGTCAGC May be for eye color
Eye color gene
Dimples gene
Hair color gene
DNA STRUCTURE
•We get our genes from our
parents, therefore they must
pass their genes (DNA) to us
How do they do this without
losing their own DNA?
DNA REPLICATION
•They must make
copies to pass on!
•DNA Replication:
The process where
DNA molecules
make an exact copy
of itself
DNA REPLICATION
RNA: The other
nucleic acid
There are 2 types of nucleic acids:
DNA- deoxyribonucleic acid
sugar: deoxyribose
double stranded
N-bases: ATCG
RNA- ribonucleic acid
sugar: ribose
single stranded
N-bases: AUCG (Uracil instead of Thymine)
There are 3 differences btwn them!
Protein Synthesis:
Remember: DNA contains the code for
making proteins (protein synthesis)
Protein synthesis (2 steps):
1.) Transcription (nucleus): a copy of
DNA is made on mRNA (messenger RNA)
2.) Translation (ribosomes): The
instructions of mRNA are translated into an
amino acid sequence of a protein
Protein Synthesis:
The Central Dogma
Protein synthesis:
The leading roles
3 types of RNA:
1) mRNA (messenger): carries
DNA directions
2) tRNA (transfer): transfers
amino acids
3) rRNA (ribosomal): composes
the ribosome
Transcription:
Reading DNA
•Transciption makes a copy of
DNA on mRNA.
•
Happens in the nucleus
•mRNA serves as a copy of DNA
that carries the instructions for
making a protein
•
Happens in the ribosomes
Translation
• Translation makes proteins in the
ribosomes from amino acids in the cell
•The instructions from mRNA are
interpreted by ribosomes to put together
the amino acids into a protein
Mutations:
When something goes wrong!
•Mutation: A change in DNA
•3 main types of mutations:
1.) Chromosomal Mutations:
changes in a chromosome
2.) Point Mutation: a change in a
single base pair
3.) Frameshift Mutation: a
mutation in which a single base
is added or deleted
Point Mutations
•Less serious than a frameshift mutation
•May change 1 amino acid
•Ex.
THE DOG BIT THE CAT
•THE DOG BIT THE CAR
•Types of point mutation
•Missense: 1 base changes and causes one amino acid to
change
•Nonsense: 1 bases changed but codes for a STOP codon
•Silent: 1 base changes, but doesn’t change the amino acid
Frameshift Mutations
•More serious than a point
mutation
•Can change several amino acids
•Ex. THE DOG BIT THE CAT
TED OGB ITT HEC AT
Mutations
THE FAT CAT ATE THE RAT
Point Mutation
THE FAT CAR ATE THE RAT
What type of mutation occurred?
Mutations
THE FAT CAT ATE THE RAT
Frameshift Mutation
THE FAT CAT CAT ETH ERA T
What type of mutation occurred?
Insertion or deletion?
Insertion!
Mutations
Mutations
THE FAT CAT ATE THE RAT
Frameshift Mutation
THE FAT CAT TET HER AT
What type of mutation occurred?
Insertion or deletion?
Deletion!