Transcript Unit 1 Ch. 1, 17, 18. WHAT IS BIOLOGY?

DNA
(Deoxyribonucleic Acid)
 What

is it?
Read Chap 13
How

Read Chap 14
How

does it work?
do we know?
Read 13, 14 & class notes
The Central Dogma
DNA makes PROTEINS and PROTEINS make LIFE
The Central Dogma
DNA makes PROTEINS and PROTEINS make LIFE
 But
how?
 At its essence, DNA is a set of instructions
for making proteins.

“DNA is a cookbook and the genes are recipes”
 Proteins
are made from different
arrangements of protein building blocks
called Amino Acids.
 There are 20 different Amino Acids. You get
them from your food.
So how do you change the protein in a tuna fish sandwich
into human hemoglobin, hair, enzymes, etc.???
There’s a little problem here…
Step 1: Transcription
Copying the DNA
DNA g mRNA
Transcription: Copying the DNA
DNAgmRNA
Transcription: Copying the DNA
DNAgmRNA
COMPARISON OF DNA AND MESSENGER RNA
Transcription: Copying the DNA
DNAgmRNA
COMPARISON OF DNA AND MESSENGER RNA
DNA
mRNA
Structure
Double
Helix
Single
Strand
Sugar
Deoxyribose
C5 H10 O4
Ribose
C5 H10 O5
Bases
A,G,C,T
A,G,C,U
Uracil
How can 4 bases tell you how to make
proteins from 20 amino acids???
 Law
of Parsimony (The simplest answer is often the right
answer. Sort of, not always but a lot.)

4 letter alphabet making 1–letter words?

4-letter alphabet making 2-letter words?
A
G
AA
GA
CA
TA
AG
GG
CG
TG
AC
GC
CC
TC
AT
GT
CT
TT
C
T
mRNA & Codons
The 3-base units of information on mRNA are
called codons.
AAU,GCC,CAU,GGG,CGA…………….
Codons “spell out” the names of the specific amino acids to
be used in making a specific PROTEIN.
The sequence of bases on DNA or RNA is called, duh,
the “base sequence”
The Universal Genetic Code is 64 triplets
It’s a 4-letter alphabet that makes 64 3-letter words
Protein Synthesis (makin’ proteins)
So this movie requires another actor… TRANSFER RNA (tRNA)
Transfer RNA (tRNA)
Protein Synthesis
 Some





terms that you MUST know…
DNA codes or triplets (the genetic code of DNA)
TRANSCRIPTION (of DNA to make mRNA)
mRNA CODONS (3-base information units of mRNA
tRNA ANTICODONS (anticodons pair with codons)
TRANSLATION (tRNA reads mRNA to make a protein)
OK, so you want to make some protein…
Hook together
AMINO ACIDS
with
PEPTIDE BONDS
Protein Synthesis = Translation
(makin’ proteins)
Codons
Transfer RNA (tRNA)
“Picks up and transfers the amino acids over to the ribosome and mRNA”
tRNA Structure
codon in mRNA
anticodon in tRNA
amino
acid
Fig. 14-7, p.223
Protein Synthesis (makin’ proteins)
“Poly-ribosomes”
Transcription
Overview
mRNA
Mature mRNA
transcripts
Translation
rRNA
ribosomal
subunits
tRNA
mature
tRNA
binding site for mRNA
P (first
binding
site for
tRNA)
A (second
binding
site for
tRNA)
c Initiation ends when a large and small
ribosomal subunit converge and bind together.
elongation
Amino
Acid
1
d The initiator tRNA
binds to the ribosome.
e One of the rRNA
molecules
b Initiation, the first stage of translating
mRNA, will start when an initiator tRNA
binds to a small ribosomal subunit.
initiation
a A mature mRNA
transcript leaves the
nucleus through a pore
in the nuclear envelope.
Fig. 14-9a-e, p.224
f The first tRNA is
released
g A third tRNA
binds with the next
codon
h Steps f and g are
repeated
termination
i A STOP codon moves
into the area where the
chain is being built.
j The new polypeptide
chain is released from the
ribosome.
k The two ribosomal
subunits now separate,
also.
Fig. 14-9f-k, p.224
and all this requires just 28 molecules…
20
5
2
1
THE END. TEST NEXT TIME.
Extra slides below.
 Disregard
the remaining slides…
Hershey
and
Chase
REPLICATION OF DNA