Download DNA vs. RNA

• Human chromosomes: 50->250 million base
pairs.
• Average gene: 3000 base pairs.
• <5% of DNA codes for protein.
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What is a Gene?
Short stretch of DNA on chromosome.
• Two parts:
•
Regulatory
region
Coding
region
DNA
Information in genes used to make proteins.
• Two Stages:
•
• Transcription
• Translation
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12-3 Protein Synthesis
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DNA
vs.
Double stranded
 Sugar = deoxyribose
 Thymine (no Uracil)

Stays in nucleus
 One type







Same copy in the cell all 
the time
RNA
Single stranded
Sugar = ribose
Uracil (instead of
Thymine)
Nucleus & cytoplasm
3 types (mRNA, tRNA,
rRNA)
Disposable copies
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Ribose vs. Deoxyribose
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RNA
 many
functions but mostly just
protein synthesis
 three
main types of RNA: messenger
RNA, ribosomal RNA, and transfer
RNA
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Types of RNA
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mRNA
RNA molecules that carry copies of the
DNA instructions = mRNA
 messenger RNA (mRNA) = serve as
“messengers” from DNA to the rest of the
cell

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Transcription & Translation
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Transcription (DNA  mRNA)
RNA molecules are produced by copying part of the
nucleotide sequence of DNA into a
complementary sequence in RNA
 required enzyme = RNA polymerase
1. RNA polymerase binds to DNA (in nucleus)
2. separates the DNA strands
3. RNA polymerase then uses one strand of DNA as a
template
4. nucleotides are assembled into a strand of mRNA
 Transcription Animation

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TRANSCRIPTION
Similar to DNA replication, but different.
1. Copies only one of the two strands.
2. Makes a copy as RNA, not DNA.
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Where does RNA start?
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Need punctuation to identify where coding
region begins and ends:
 promoters - signals in DNA that indicate
where the enzyme should bind (“start
sequence”).
 Similar signals in DNA cause transcription to
stop when the new RNA molecule is
completed.

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RNA Editing
Intron = intervening sequence of DNA; does
not code for a protein
 Exon = expressed sequence of DNA; codes
for a protein
 When RNA molecules are formed, both the
introns and the exons are copied from the
DNA

– introns are cut out of RNA molecules while they
are still in the nucleus
– exons are then spliced back together to form the
final mRNA
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The Genetic Code
Proteins = long chains of amino acids
(polypeptides)
 polypeptide = combination of any or all of
the 20 different amino acids
 properties of proteins are determined
by the order in which different amino acids
are joined together to produce
polypeptides

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The “language” of mRNA instructions is
called the genetic code
 RNA contains four different bases: A, U, C,
and G
 Letters read “3” at a time = codon
 Codon = a group of three nucleotides on
messenger RNA that specify a particular
amino acid.

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Translation
(mRNA tRNA amino acid chain)
 Occurs
at the Ribosome
 mRNA = instructions for the order
of the amino acid sequence
 Ribosome = reads the instructions
of the mRNA
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Translation
DNA/RNA
Adenine
Cytosine
Guanine
Thymine/Uracil
Amino Acid
Alanine
Arginine
Asparagine
Aspartate
Cysteine
Glutamine
Glutamate
Glycine
Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Proline
Serine
Threonine
Tyrosine
Tryptophan
Valine
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rRNA

Ribosomes are made up of several dozen
proteins, as well as a form of RNA known
as ribosomal RNA (rRNA).
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tRNA

During the construction of a protein, a third
type of RNA molecule transfers each amino
acid to the ribosome
– as specified by coded
messages in mRNA.

These RNA molecules
are known as
transfer RNA (tRNA).
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Identify the players at work
3
1
2
4
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Steps of Translation
mRNA is released from the nucleus 
enters cytoplasm
2. mRNA attaches to the ribosome
3. mRNA codons move through the
ribosome proper amino acid brought by
tRNA
4. Amino acids are bound together 
polypeptide chain
1.
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
Each tRNA carries only one type of amino
acid

The three bases on tRNA = anticodon
(complementary to mRNA)
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The ribosome forms peptide bonds
between the neighboring amino acids
 It also breaks the bonds between tRNA and
the amino acids
 Translation ends when a “stop” codon is
reached

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 Translation
Animation
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Bases in DNA/RNA form triplet code
Codon Table:
U
U
First base
A
G
GUU
GUC
GUA
GUG
Phe (F)
Leu (L)
Leu (L)
Ile (I)
Met (M)
Start
Val (V)
UCU
UCC
UCA
UCG
CCU
CCC
CCA
CCG
ACU
ACC
ACA
ACG
UAU
Tyr (Y)
UAC
UAA
Stop
UAG
Stop
CAU
His (H)
CAC
Pro (P)
CAA
Gln (Q)
CAG
AAU
Asn (N)
AAC
Thr (T) AAA
AAG Lys (K)
Ser (S)
GCU
GCC
Ala (A)
GCA
GCG
GAU
GAC
GAA
GAG
Asp (D)
Glu (E)
G
UGU
Cys (C)
UGC
UGA
Stop
UGG Trp (W)
CGU
CGC
Arg (R)
CGA
CGG
AGU
Ser (S)
AGC
AGA
AGG Arg (R)
U
C
A
G
U
C
A
G
U
C
A
G
GGU
GGC
GGA
GGG
U
C
A
G
Gly (G)
Third base
C
UUU
UUC
UUA
UUG
CUU
CUC
CUA
CUG
AUU
AUC
AUA
AUG
Second Base
C
A
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What amino acids are made?
Use the mRNA strand on the Genetic Code
Chart
 DNA: TAC AAA CAC GGA CCA ACT
(coding strand)
 mRNA: AUG UUU GUG CCU GGU UGA
 tRNA: UAC AAA CAC GGA CCA ACU
 Amino acids: Methionine – Phenylalanine –
Valine - Proline - Glycine - STOP

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