Download Watson and Crick

Biology
DNA Unit
PDE Big Idea 8A
The basic molecular and the associated
genetic code structure of DNA are universal,
revolutionizing our understanding of disease,
heredity, and evolution.
Griffith’s Experiments
• Frederick Griffith did a series of
experiments with Streptococcus
pneumoniae (pneumonia) in 1928.
• He noticed that one strain (the S
strain) of the bacteria caused
disease, the other (the R strain)
didn’t.
Griffith’s Experiments
• Griffith did four experiments using
mice and various mixtures of the
disease causing and non disease
causing bacteria.
Experiment 1
• He injected a mouse
with live S strain
bacteria.
• As a result, the mouse
died.
Experiment 2
• He injected a mouse
with live R strain
bacteria.
• As a result, the mouse
lived.
Experiment 3
• Mouse was injected
with heat killed S
strain cells
• The mouse lived
Experiment 4
• Mouse was injected
with heat killed S
strain cells and live
R strain cells
• The mouse died
Griffith’s Conclusion
• Griffith concluded that
there was some
hereditary factor
released by the dead S
cells and absorbed by
the live R cells
• Today we call this
transfer of genetic
material from one
organism to another
transformation
Avery’s Experiment
• Oswald Avery later did
three experiments in
which he used enzymes
to deactivate protein,
RNA and DNA and
injected them into mice
• He found that DNA was
the hereditary factor
from Griffith’s
conclusion
Watson and Crick
• James Watson and
Francis Crick discovered
the double helix shape
of DNA in 1953
DNA Anatomy
• Further studies of DNA
showed that it contains
three parts
1. Deoxyribose (sugar)
2. Phosphate
3. A nitrogenous base
- Put all three parts
together and you have
a nucleotide, the
building blocks of
DNA
Nucleotides
• The four nucleotides of
DNA are known as
Adenine (A), Guanine
(G), Cytosine (C) and
Thymine (T)
• RNA also has
nucleotides, but
Thymine is replaced
with Uracil (U)
Purines and Pyrimidines
• Purines have 2 rings and Pyrimidines have 1.
• Purines and Pyrimidines Hydrogen bond to
one another
Base Pairing
• Because of the bonding
pattern of the purines
and pyrimidines, how
the bases pair up can
easily be predicted
• C and G always pair up
• In DNA, A and T pair up
• In RNA, A and U pair up
G–C
A–T
C–G
T–A
G–C
A–U
C–G
U–A
DNA and RNA Functions
• DNA contains the
directions for making all
of the proteins in the
body, but it can not leave
the nucleus
• RNA is made from DNA
and contains selected
information from the
DNA
• RNA leaves the nucleus
and is used to make
protein in the cytoplasm
Replication
- The process in which copies of DNA are made
- The enzyme helicase unzips the DNA into two
separate strands.
- New strands are then built onto the old
strands
- Each new double helix has half of the old one
- Because of this, we say that the process is
conservative
Replication Example
Old Strand
New Strand
GATTACATCCGTA
CTAATGTAGGCAT
Transcription
• This is when DNA is
used to make RNA,
which will be used to
make protein
• The base thymine (T) is
replaced with uracil (U)
Transcription Example
DNA Strand
RNA Strand
GTAC GCTAT TCG
CAUGCGAUAAGC
Transcription Makes Three Main
Types of RNA
• mRNA – the
blueprint for making
protein (messenger)
• tRNA –
(transfer)carries
amino acids to
ribosomes (transfer)
• rRNA – becomes
part of the ribosome
(ribosomal)
Translation
• Making protein from
RNA
• mRNA is read by the
ribosome (part rRNA)
in order to construct a
new protein made from
amino acids which are
supplied by the tRNA
mRNA
• In order to determine
the order of the amino
acid sequence,
scientists had to crack
the genetic code
• Within the mRNA there
is a code that specifies
what amino acid goes
where in the protein
Codons
• Examples:
AGA = arginine
GGA = glycine
UGC = cysteine
* See page 207 in your
textbook
• Scientists found that
the mRNA was
organized into
segments 3 bases long,
that they called codons
• Each codon specifies an
amino acid
• The genetic code has a
lot of repetition
Start Codon
• Transcription often
makes long strands of
mRNA that may have
directions for many
proteins
• The cell needs to know
where to begin
translating
• The “on switch” is
known as the start
codon
Start Codon = AUG
AUG = methionine
Stop Codons
• The cell also needs to
know where to stop
translating
• Because of this there
are 3 “off switches” or
stop codons
• They are UAA, UAG and
UGA
Anticodons
• The tRNA knows where
to attach to the mRNA
because it contains the
complimentary bases
to the codon
• These bases are called
an anticodon
Codon
AUG
GAC
UCA
Anticodon
UAC
CUG
AGU
Translation
• mRNA slides between the large and small
subunit of a ribosome until AUG is found
Translation
• A tRNA brings in the necessary amino acid
and its anticodon binds to the codon
Translation
• The next codon slides through the ribosome
Translation
• The next tRNA brings its amino acid. Its
anticodon binds to the codon and a peptide
bond forms between the amino acids.
Translation
• The next codon slides through the ribosome
and the first tRNA is released.
Translation
• The process continues over and over again
until a stop codon is reached. Then the
polypeptide is released and the ribosome can
start over.
Transcription/Translation Practice
DNA
AGTACGCTTCGACTGT
mRNA U C A U G C G A A G C U G A C A
Protein Structure
• After proteins are
made, they often bend,
twist, fold and interact
with other proteins to
make a useable
product for an
organism
Primary Protein Structure
• This refers to the order
of the amino acids in
the polypeptide
(protein) chain
Secondary Protein Structure
• Certain amino acids
have charged regions
and will form hydrogen
bonds
• This causes the protein
chain to fold, twist or
change shape in some
way
Tertiary Protein Structure
• Most protein chains
include many different
features (twists, sheets,
and folds)
• The final 3-dimensional
shape of the entire
protein is the tertiary
structure
Quaternary Protein Structure
• In many cases,
different proteins will
bind together to make
a final product
• Quaternary structure is
the interaction
between two or more
protein chains
Enzymes
• Enzymes are special proteins that catalyze
(speed up) chemical reactions
• The beginning substances they work on are
called substrates
• The substrates are changed into different
molecules
Enzymes
• Enzymes catalyze more than 4,000
biochemical reactions
• Enzymes are essential to the survival of many
organisms
• For example, without them we could not
digest our food, get rid of carbon dioxide or
send messages through our nerves
How Enzymes Work