1. DNA, RNA, and Gene
Expression
Biology 163
Unit 5 DNA and Genetic Engineering
Chapters 12, 13, & 15

2. DNA Structure and
Components


Double Helix – 2 strands form a
twisted ladder
Subunits of nucleotides contain:




Sugar – deoxyribose
Phosphate Group (PO4-)
Nitrogen Base
Backbone (“uprights”) made of
deoxyribose and phosphate

3. Nitrogen Bases

Purines – 2 rings



Pyrimidines – 1 ring



Adenine
Guanine
Thymine
Cytosine
Order of bases contains
the “code” to make
proteins

4. DNA Structure and Components
- Phosphate Group (PO4-)
Purines
(2 rings)
DNA Nucleotides
Adenine
Guanine
- Nitrogen Base
Thymine
Pyrimidines
(1 ring)
Sugar: Deoxyribose
- 5 carbons
-
Cytosine

5. DNA Base Pairing



Adenine pairs with
Thymine
Guanine pairs with
Cytosine
Bases (“rungs”) are
connected by
hydrogen bonds

6. Discovering DNA

Many scientists worked to understand the
DNA structure
Source of DNA
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human

A
30.9
29.4
19.9
19.8
Chargraff’s rule: [G] = [C] and [A] = [T] ;

7. Discovering DNA


1952 - Rosalind
Franklin studied
DNA using x-ray
1953 – James Watson
and Francis Crick
determined the double
helix structure

8. DNA and Chromosomes
Chromosome
Nucleosome
DNA
double
Coils
Supercoils
Histones –
proteins which DNA
is wrapped around
helix

9. Replication
Fork
DNA Replication

DNA replicates during
S phase of interphase



DNA
Polymerase
2 copies needed for
mitosis
New Strand
New
Each strand serves as Strand
a template for the new Origina
l
strand
Strand
Replication
Fork
Results in 2 identical
DNA molecules
Nitrogen
Bases
Original
Strand
DNA
Polymerase

10. DNA Replication
1) Parent DNA has
complementary
strands
2) H bonds break,
“unzipping” the
DNA
3) Using the parent
strand as a
template, new
DNA strands
form -DNA
polymerase
4) New backbones
form – two new
DNA molecules

11. DNA Replication

Semi-conservative
replication – each new
molecule contains one old
strand and one new strand
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter14/
animations.html#

12. RNA Structure and
Composition


RNA – ribonucleic acid
Nucleotides made of:




Ribose
Phosphate group
Nitrogen Bases
Same bases as DNA
except uracil instead of
thymine

13. DNA vs. RNA
DNA
RNA
Type of Sugar
Deoxyribose
Ribose
# of Strands
2
1
Nitrogen Bases
A, C, T , G
A, C, U , G
Nucleus only
Nucleus, cytoplasm,
or ribosome
Location in the
Cell

14. Types of RNA
mRNA
“messenger”
tRNA
“transfer”
rRNA
“ribosomal”
made using DNA
transfers an amino
acid to the growing
protein
makes up the
bulk of ribosomes
carries genetic info
from the nucleus to
the ribosome
every 3 bases
(codon) specifies
an amino acid
cloverleaf shape
3 complimentary
bases (anticodon)
binds to the mRNA
codon

15. Protein Synthesis: two parts!

Transcription: DNA mRNA


occurs in the nucleus
Translation: mRNA  protein

occurs on the ribosome (in the cytoplasm)

16. Transcription (RNA Synthesis)



One strand of DNA
serves as a template for
the synthesis of mRNA
Occurs in the nucleus
RNA polymerase
joins RNA nucleotides

17. Translation (mRNA to Protein)





mRNA attaches to ribosome
Each tRNA carries one amino
acid
Anticodon on tRNA
matches with a codon
on mRNA
Amino acids join forming a
polypeptide chain
Long polypeptide chains
form protein!!!

18. Protein
Synthesis
Summary

19. How does DNA “code” for protein?


Each codon codes for
1 of 20 amino acids
What amino acid chain
would form from the
mRNA:
AUGGUCCAA
Met–Val–Glu

20. The Genetic Code


64 different
combinations of
RNA bases
1 “start” codon


Methionine
3 “stop” codons

21. Mutations… oops!



Mutations can be harmful or helpful
May lead to cancer or genetic disorders
May result in a new positive trait
Deletion
Duplication
Inversion
Translocation