Download D.N.A.

D.N.A. is a Nucleic Acid
D.N.A is capable
of……
• carrying genetic
information to next
generation
• directing the cell
to follow its orders
• being easily
copied
History of the Discovery of D.N.A

1952 – Rosalind Franklin studies the
DNA molecule using a technique called
X-ray diffraction.
History of D.N.A. Cont’d.

Watson and Crick
 They used Rosalind Franklin’s pictures of DNA to figure out the structure of
D.N.A.
 established the structure as a double helix - like a ladder that is twisted. The
two sides of the ladder are sugar phosphate backbone and are held together
by hydrogen bonds.
Basic Structure of D.N.A.
The sides of D.N.A.
alternate Sugar and
Phosphate. (sides
of the ladder)
 The bases make up
the middle (rungs of
the ladder)
A–T
C-G

DNA: Deoxyribonucleic acid

The building blocks of DNA are nucleotides, each
composed of:
 a 5-carbon sugar called deoxyribose
 a phosphate group (PO4)
 a nitrogenous base (4 types)
○ Adenine (A), thymine (T), cytosine (C), guanine (G)
Phosphate
group
Deoxyribose (sugar)
Nucleotide!
DNA Structure

The two strands of
nucleotides are
antiparallel to each other
 one is oriented 5’ to 3’, the
other 3’ to 5’

Basically, one side runs
“right side up and one
side runs upside down”.
7
The 4 Bases

Bases come in two types:
1. Pyrimidines (cytosine and thymine) – Have one
ring of carbon
2. Purines (guanine and adenine) – Have two rings of
carbon

Purines pair with Pyrimidines:
 Adenine with Thymine
 Guanine with Cytosine
DNA Chromosome Structure
Think back: When did we learn that DNA had to be
replicated??
During the cell cycle in S phase
DNA Replication
Replication Steps:
1. DNA unzips
2. New nucleotides assemble
3. Two new strands of identical DNA are
reproduced – each with one original stand.
Replication Enzymes

2 Main enzymes involved

1. Helicase – unzips the DNA to
the replication forks
2. DNA polymerase
 It has two main functions.
○ 1. Adds new bases
○ 2. “proofreads”

The Big Picture
When we want
to make a
protein we
have to transfer
the “code” from
DNA on to a
special
molecule called
RNA!
 This is called
Transcription.

So how do we get from the code
from the bases to really make
us a protein?
RNA
RNA stands for Ribonucleic
Acid.
 It is a special molecule that
carries the code from DNA
out to the ribosomes so that
we can make the right
protein.
 It is our messenger!!
 Notice how it is different
from DNA.

RNA
Similarities
 Phosphate
 Sugar
 Base
Differences
 Sugar is ribose (DNA:
deoxyribose)
 Single stranded (DNA:
double helix)
 Has uracil as a base, not
thymine
 It can travel outside of the
nucleus.
Transcription

Transcription is the process of copying
the code of DNA into RNA so it can go to
the ribosome and make protein.
Transcription
takes places in
the NUCLEUS
A-U
C-G
T-A
Transcription
3 STEPS
1. RNA polymerase (another enzyme) binds to the promoter region
of DNA
2. RNA polymerase unzips the DNA and adds nucleotide bases
A-U, C-G
3. RNA polymerase stops when it comes to a termination region of
DNA
Let’s see this in
action: http://wwwclass.unl.edu/bioch
em/gp2/m_biology/
animation/gene/ge
ne_a2.html
Practice/Review
So if one side of DNA has the following
bases, what would the other side have?
A C T G G T A C G A T A
T G A C C A T G C T A T
Using the original strand above, what
would the RNA strand look like?
U G A C C A U G C U A U

Translation
Now that we have our
mRNA it is time to make a
protein…..we do this at the
ribosome.
Translation –
converting the
code in mRNA
into a protein.
To do this we use a
special molecule
called transfer
RNA
Transfer RNA




Transfer RNA (tRNA) looks
like a cross. It has three
bases that attach at the
bottom.
We call these anti-codons.
They attach to three bases on
the mRNA which we call
codons.
At the top of the tRNA is an
amino acid (the building block
of proteins)!!
Translation
Steps – 8 easy steps!!
1. The newly made mRNA travels to the ribosome.
2. The ribosome reads the mRNA code in groups of three, called
“codons.” Starts at AUG
3. tRNA anticodons match up with the mRNA codons.
4. Another tRNA attaches to the next codon. Its amino acid is
attached to the previous one.
Translation
5. The first tRNA falls off
6. The ribosome moves along
the mRNA, using tRNA to
attach amino acids.
7. The process ends when a stop
codon is reached (UGA, UAA,
UAG).
8. The amino acid chain is
released – it folds into a 3-D
structure called a protein.
Amino Acid Chart

So how do we know what amino acid is at the top of each transfer
RNA? We use this cool chart. Start at the middle and work towards
the outside.
This chart
is based
on mRNA
codons!!
Practice:
1. UCC
Serine
2. AAG
Lysine
3. UAA
Mutations
Mutations
are changes in the DNA sequence that affect
genetic information
Types of gene mutations (changes in a single gene):
 Substitution
○ Original strand: TAC GCA TGG
○ Mutated strand: TAC GTA TGG
 Insertion
○ Original strand: TAC GCA TGG
○ Mutated strand: TAT CGC ATG
 Deletion
○ Original strand: TAC GCA TGG
○ Mutated strand: TCG CAT GG
Insertions
and deletions cause the biggest problems b/c
Mutations
Types
of chromosomal Mutations
(changes in whole chromosomes):