CHAPTER 13:
DNA, RNA, and Proteins
Essential Questions:
What is DNA?
How is DNA related to
traits?
What is the Central
Dogma of Biology?
Who discovered DNA?
DNA- The Genetic Material
• Why should I care about DNA?
• DNA stores the information that tells cells which proteins to make
• Your proteins give you your physical/chemical/ identity
• Your DNA is different from everyone else’s DNA on earth
Does DNA have anything to do with why I am
so special?
• Yes, it’s the variability of DNA that makes us
all different!
The Central Dogma of Biology
DNA
RNA
PROTEINS
DNA is transcribed into RNA
RNA is translated into Proteins
Proteins give you your traits or Phenotype
Searching for the Genetic Material
• Griffith - Discovered the
transformation of harmless R
strain Bacteria by heat killed S
bacteria
• Avery – Identified DNA as the
transformative agent
• Hershey & Chase –Studied
bacteriophages and proved
DNA was the source of
hereditary information
Who Discovered the Structure of DNA?
 James Watson & Francis Crick discovered the
structure of DNA after observing an X-ray
picture of it taken by Rosalind Franklin
Structure of DNA
Structure of DNA
DNA is an Alpha
Double Helix
Composed of two
strands of nucleotides
Joined like a twisted
ladder by hydrogen
bonds
The Structure of DNA
The Structure of DNA is both complex and
simply elegant
DNA is a polymer of Nucleotidesremember a polymer is like a chain of
beads- DNA is made of 2 chains
There are 4 different Nucleotides (beads)
abbreviated as A, T G, or C
The Base on one chain “complements” and
makes a bond with the base on the opposite
chain
The bases are bound together by hydrogen
bonds.
The two strands are twisted together
DNA Structure
DNA is a polymer of nucleotides (the beads on the chain)
Each Nucleotide contains
1 Nitrogenous base + 1 phosphate group + 1 sugar
In DNA the sugar is deoxyribose
Nucleotide
Nitrogenous Bases
The Structure of DNA
There are 4 different Nucleotides
identified by their Nitrogenous Bases:
Adenine Guanine (the purines)
Cytosine Thymine (the pyrimidines,)
The Bases are said to “complement” one
another - A bonds to T, G bonds to C
according to the base pairing rules(also
called Chargraffs Rules)
The bases are bound to each other by
hydrogen bonds.
The Structure of DNA
The DNA Double Helix is
composed of 2 interconnected
nucleotide chains
The nucleotide chains are
composed of a SugarPhosphate backbone, with
bases in the middle
The Nucleotides are joined by
Phosphodiester bonds
DNA Replication
DNA Replication
Why does DNA replicate?
Cells get worn out, new cells must be made
New cells must make exact copies of themselves
Copies of replicated genes can be passed on to
offspring
How is DNA Replicated?
Helicase breaks hydrogen bonds in the middle of the
strand, creating a replication fork
Unpaired bases form new bonds with free nucleotides in
the cell with help form DNA Polymerase
New strand is rewound together by DNA Polymerase,
creating 2 identical DNA molecules
Fun Facts about Replication?
Sometimes replication errors occur
(A bonds to a G)
There are 3 x 109 base pairs in the average
human cell
It takes about 4 hours for a cell to replicate its
DNA - -Multiple forks start simultaneously
The process is SEMI-Conservative, IE each
new DNA molecule has one old strand
Transcription
Understanding DNA
Replication can help you
to understand
transcription. (DNA
copying!)
Instead of multiple
enzymes, transcription
use only RNAPolymerase
(RNAPol)
http://www.dnalc.org/resources/3d/12-transcription-basic.html
The Central Dogma of Biology
DNA is transcribed into RNA
RNA is translated into Proteins
Proteins give you your traits or
Phenotype
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Transcription
DNA is located in the
nucleus of the cell
DNA CANNOT leave the
nucleus of the cell
because it is AN
EXTREMELY LARGE
MOLECULE
So How does it get out?
http://www.dnalc.org/resources/3d/12-transcription-basic.html
Transcription
Mr. Dougherty! I am afraid for the DNA, it can’t get to the ribosome to
be translated!
What will it do?
Relax, RNA is the key!
Imagine the nucleus is like a library,
where each book is a gene.
…but you can’t take any books out!
You could make copies of the books…
That’s how RNA works
http://www.pbs.org/wgbh/no
va/body/rnai.html
What is RNA?
•A nucleic acid that is similar to
DNA
•Ribose is the sugar
•Instead of thymine, Uracil
•Single stranded
Steps of Transcription
1. DNA strand unwinds via RNAPolymerase (not helicase)
2. Free nucleotides bond to bases, except U in RNA bonds to A
from DNA
3. RNA polymerase joins single stranded RNA together
4.Messenger RNA (mRNA) moves to the ribosome in the cytoplasm
(or on the Rough ER)
Translation
Translation (Protein Synthesis)
What is protein synthesis?
The Conversion of RNA to
Amino Acids
which make up proteins
Why is it called translation?
The genetic code (ATCG) is
translated
into a protein
Where does it occur?
At the ribosome in the cytoplasm
Globular Protein found in Human Blood
(serum albumin)
Translation and the Genetic Code
RNA is composed of 3 letter
“words” called CODONS
Each codon of RNA represents
a specific Amino Acid
For instance AUG is the start
codon, and UUU represents
the amino acid Phe
(phenylalanine)
Why is it called translation?
The genetic code (ATCG) is
translated
into a protein
Genetic Code
Problem
If the DNA code is
AAT GCG TTT CGC ATA TAT
Then the RNA compliment is
___ ___ ___ ___ ___ ___
and the Amino Acid sequence that
results is
____ ____ ____ ____ ____ ____
How Does Translation Occur?
The 3 Steps of Translation
1. Initiation
A. Ribosome attaches to mRNA (each 3 bases
is called a codon)
B. tRNA brings anticodon and AA to ribosome
2. Elongation
A. More tRNA’s bring more AA’s to
ribosome
B. AA’s connected together to make
polypeptides (by peptide bonds)
3. Termination
A. Ribosome reaches a STOP signal on
mRNA
B. Polypeptide (protein) is broken off and
becomes part of the human body
C. Golgi apparatus modifies completed
protein; ER transports it in/out of cell
Translation
http://www.youtube.com/watch?v=5bLEDd-PSTQ
Translation Animation
The processes of transcription and
translation are the same in all living
organisms!
Blue Whale
Tarantula