GENE
EXPRESSION
What is DNA Replication?
• DNA Replication – the
process of creating copies of
DNA molecules
Why is DNA Repliction SEMI
CONSERVATIVE?
– DNA Replication is SEMICONSERVATIVE (each
strand of the original DNA
molecule serves as a
template for the two new
DNA molecules)
One ring
O
N
O
C
C
N
C
N
N
C
thymine
C
O
C
C
C
N
C
cytosine
• Thymine and cytosine each have one ring
Two rings
N
N
C
O
C
N
C
C
N
N
C
Adenine
N
N
C
C
N
C
N
C
Guanine
C
N
• Adenine and guanine each have two rings
Hydrogen Bonds
• When making
hydrogen bonds, a
double ring always
pairs with a single
ring
• A–T
• C–G
O
N
O
C
C
C C
N
N
C
N
C
C
N
C
N
C
N
C
DNA Replication: Simplified
DNA Replication = 3 steps
What are the 3 steps of DNA
Replication?
DNA Replication = 3 steps
1. Unzip DNA
2. Add free nucleotides
3. Re-zip new strands to old strands
Enzymes Play an Important Role!
Many enzymes help DNA replicate
 Enzymes are proteins
• Enzyme #1 = helicase
(unwinds DNA)
Enzymes Play an Important Role!
Many enzymes help DNA replicate
 Enzymes are proteins
• Enzyme #2 = DNA Polymerase
(add new nucleotides, “proofreads”
for mistakes
So...exactly HOW do we use our
DNA?
• Our DNA sequences serve as a code!
• ACTGGGACTACCATTGA
• We take this information and make RNA
molecules, which help us to make
proteins!
DNA Review:
Try to fill in the blanks:
1. A nucleotide is made of three parts:
______________ , __________________,
and one of the _______ pairs.
2. The nucleotides are combined together to
create a __________ acid, and ______ is
an example of this.
Review:
1. A nucleotide is made of three parts:
DEOXYRIBOSE SUGAR__ ,
_PHOSPHATE_, and one of the __BASE _
pairs.
2. The nucleotides are combined together to
create a _NUCLEIC_ acid, and _DNA_ is
an example of this.
More about Nucleic
Acids!
• We’ve already learned about
one important nucleic acid,
DNA. Today, we’ll explore the
second nucleic acid…
• RNA!!
RNA NOTES
How is RNA different from
DNA?
Three differences from DNA:
1. RNA = one strand (DNA = two strands)
2. RNA has the sugar ribose (DNA has the
sugar deoxyribose)
3. RNA uses uracil [U] instead of thymine
(DNA = A, T, G, C RNA = A, U, G, C )
DNA
vs.
Deoxyribose Sugar
Double Stranded
(usually)
THYMINE base
1 type of DNA
RNA
Ribose Sugar
Examples of
Nucleic Acids
Made of
Nucleotides
Code for
Information
Single Stranded
(usually)
URACIL base
3 types of RNA
(mRNA, rRNA, tRNA)
DNA
RNA
What are the 3 types of
RNA?
3 types of RNA:
• Messenger RNA
(mRNA) carries the
genetic message
• Transfer RNA (tRNA)
transfers amino acids
• Ribosomal RNA
(rRNA) makes
ribosomes
D
N
A
Transcription
What is Transcription?
transcribe = “to copy”
The genetic code on DNA is copied to RNA in
the nucleus
Why does it happen in the
nucleus?
Original DNA cannot pass
through the nuclear
membrane, so a smaller
copy is made and
transported
• Where in the cell does transcription happen?
• The nucleus!
• Why does it happen in the nucleus?
• Original DNA cannot pass through the nuclear
membrane, so a smaller copy is made and transported
How does Transcription
happen?
1. RNA polymerase unwinds DNA
2. RNA polymerase adds RNA
nucleotides
(A  U, G  C)
3. mRNA is formed! DNA
reforms a double helix
Transcription recap…
• RNA polymerase makes RNA using DNA
sequence
• RNA leaves the nucleus for the cytoplasm
Translation
Where does it go from there?
Into the great beyond?
To a ribosome!
(Floating in
cytoplasm)
At this point you only knew
ribosome's as little dots in the cell…
now you will learn their big purpose!
Turning RNA into the
proteins that make up your
hair, skin, muscles, nails etc!
What is translation?
• Ribosomes translate
mRNA into an amino
acid sequence
• Amino acids form
proteins
What is a Codon?
Codons = 3 nucleotides in a row
How are codons
used?
Ribosome recognizes a codon
on mRNA and matches to the
aniticodon on tRNA
amino
acid
anticodon
ACG
How do tRNA and
anticodons work together?
Transfer RNA transfers amino acids from the
cytoplasm to a ribosome
amino
acid
Anticodon = 3 nucleotides on
one end of a tRNA
anticodon
ACG
Anticodons base pair with complementary
bases on mRNA
Codons
Codon triplets code for 1 of 20 amino acids
Codons
1 “start” codon
3 “stop” codons
Steps of Translation
1. mRNA attaches to ribosome
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
mRNA
Steps of Translation
2. tRNAs add amino acids based on how
anticodons match to mRNA
Steps of Translation
3. Protein is released from ribosomes!
Protein chain
Stop codon
Steps of Translation
3. Protein is released from ribosomes!
Protein chain
What process turns DNA into
RNA?
•Transcription!!
What process turns RNA into
PROTEIN?
•Translation!!
What do amino acids build?
•Protein!!
Summary
DNA
(Transcription)
RNA
(Translation)
PROTEIN
Gene Expression Practice
1. DNA sequence: AAC TGA CTG ATT GCA TGC
• What is the complementary DNA sequence?
TTG ACT GAC TAA CGT ACG
• What is the complementary RNA sequence?
UUG ACU GAC UAA CGU ACG
• What are the amino acids for this sequence?
2.
DNA sequence: TAG CAT TGG GCA TCA CGA
• What is the complementary DNA sequence?
ATC GTA ACC CGT AGT GCT
• What is the complementary RNA sequence?
AUC GUA ACC CGU AGU GCU
• What are the amino acids for this sequence?
EXIT QUIZ
Determine the amino acids for this strand of mRNA:
AUG GCA AGU UCU UGA
(Use
genetic
code
table on
page
186Turtle
or p.
526)
Met – Ala – Ser – Ser – STOP
Practice
Determine the amino acids for this strand of mRNA:
UGU AGA GAU CUC UAA
Cys – Arg – Asp – Leu – STOP
(Use
genetic
code
table on
page
186Turtle
or p.
526)
Big Picture
Gene Expression Short Essay
• Take one of the gene expression pictures
and staple or tape it to a piece of paper
(you may also choose to draw this out).
• Explain in your own words how DNA is
used to make proteins including a brief
description of DNA replication,
transcription, and translation.