DNA, RNA, and Gene Expression

Biology 163Unit 5 DNA and Genetic

EngineeringChapters 12, 13, & 15

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

Nitrogen Bases Purines – 2 rings

Adenine Guanine

Pyrimidines – 1 ring Thymine Cytosine

Order of bases contains the “code” to make proteins

DNA Structure and Components

DNA

- Phosphate Group (PO4-)

-Sugar: Deoxyribose

- 5 carbons

- Nitrogen Base

Purines(2 rings)

Pyrimidines(1 ring)

Adenine

Guanine

Thymine

Cytosine

Nucleotides

DNA Base Pairing

Adenine pairs with Thymine

Guanine pairs with Cytosine

Bases (“rungs”) are connected by hydrogen bonds

Discovering DNA Many scientists worked to understand

the DNA structure

Chargraff’s rule: [G] = [C] and [A] = [T] ;

Source of DNA A T G CSource of DNA A 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 30.9 29.4 19.9 19.8

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 30.9 29.4 19.9 19.8

Discovering DNA

1952 - Rosalind Franklin studied DNA using x-ray

1953 – James Watson and Francis Crick determined the double helix structure

DNA and Chromosomes

Chromosome

Supercoils

Coils

Nucleosome

Histones – proteins which DNA is wrapped around

DNA

double

helix

DNA Replication

DNA replicates during S phase of interphase 2 copies needed for

mitosis Each strand serves

as a template for the new strand

Results in 2 identical DNA molecules

Replication Fork

New Strand

Original Strand

DNA Polymerase

DNA Polymerase

Original Strand

Replication Fork

New Strand

Nitrogen Bases

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

DNA Replication

Semi-conservative replication – each new molecule contains one old strand and one new strand

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html#

RNA Structure and Composition

RNA – ribonucleic acid Nucleotides made of:

Ribose Phosphate group Nitrogen Bases

Same bases as DNA except uracil instead of thymine

DNA vs. RNA

DNA RNA

Type of Sugar Deoxyribose

# of Strands 2

Nitrogen Bases

A, C, T, G

Location in the Cell

Nucleus only

Ribose

1

A, C, U, GNucleus,

cytoplasm, or ribosome

Types of RNA

mRNA

“messenger”

made using DNA

every 3 bases (codon) specifies

an amino acid

tRNA

“transfer”

transfers an amino acid to the growing

protein

cloverleaf shape

3 complimentary bases (anticodon) binds to the mRNA

codon

rRNA

“ribosomal”

makes up the bulk of ribosomes

carries genetic info from the nucleus to

the ribosome

Protein Synthesis: two parts! Transcription: DNA mRNA

occurs in the nucleus Translation: mRNA protein

occurs on the ribosome (in the cytoplasm)

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

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!!!

Protein Synthesis Summary

How does DNA “code” for protein?

Each codon codes for 1 of 20 amino acids

What amino acid chain would form from the mRNA:AUGGUCCAAMet–Val–Glu

The Genetic Code

64 different combinations of RNA bases

1 “start” codon Methionine

3 “stop” codons

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