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Transcription and Translation
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Standard(s):
• SC.912.L.16.5 Explain the basic processes of
transcription and translation, and how they result
in the expression of genes.
Learning objectives:
• Students will compare and contrast the processes
of transcription and translation.
• Students will model how transcription and
translation lead to the expression of genes.
DNA
RNA
transcription
translation
Amino acid
Protein
Codon/ anticodon
Guiding question:
How are proteins made
according to the code in DNA?
cell
chromosome
nucleus
DNA
gene
Transcription
Transcription
Transcription- is the process in which DNA
is unzipped in a particular gene to create a
copy (mRNA) that will code for a specific
protein needed by the cell/ living organism.
• DNA makes RNA
Transcription
• RNA polymerase “unzips” DNA
• RNA polymerase copies the nucleotide
bases from DNA to mRNA according to
the base paring rules in the 5’ to 3’
direction (adds to the 3’ end)
– C pairs with G, A pairs with T in DNA (and
U in mRNA)
Transcription
• Once completed, the newly formed
mRNA is sent to the ribosome complex
(in the cytoplasm) to make a protein
*Went from DNA to mRNA!!
Transcription in a nutshell
Occurs inside the nucleus
Specific gene is copied into mRNA (messenger)
One mRNA codes a single protein
End result is the code for a single protein
Translation
Translation- is the process of changing the
mRNA code coming from the DNA into
amino acids that will form the protein
needed by the cell/ living organism.
• RNA makes Protein
Translation
• mRNA bind with a ribosome forming a
complex in which different tRNA brings an
amino acid by matching the mRNA according
to the base paring rules for RNA.
• mRNA and tRNA (transport) function in
triplets called codon and anticodon
respectively
– Work like a key and lock system.
Codon
• Each tRNA molecule has a triplet anticodon on
one end and an amino acid attachment site on
the other
Amino acid
attachment
site
Anticodon
Figure 10.11B, C
• mRNA, a specific tRNA, and the ribosome
subunits assemble during initiation
Large
ribosomal
subunit
Initiator tRNA
P site
A site
Start
codon
mRNA
1
Figure 10.13B
Small ribosomal
subunit
2
Amino acid
Polypeptide
A
site
P site
Anticodon
mRNA
1
Codon recognition
mRNA
movement
Stop
codon
New
peptide
bond
3
Translocation
2
Peptide bond
formation
Figure 10.14
Translation
• In protein production there are codons that will
indicate to the ribosome when to start and when
to end.
• Once the chain of up to several hundreds of
amino acids is completed, the process stops and
the protein gets sent to the endoplasmic
reticulum to be packed and released.
• The order of amino acids determines the shape
and function of the newly formed protein.
Gene 1
Gene 3
DNA molecule
Gene 2
DNA strand
TRANSCRIPTION
RNA
Codon
TRANSLATION
Polypeptide
Figure 10.7
Amino acid
Virtually all organisms share the same genetic code
“unity of life”
Second Base
C
U
UUU
UUC
UUA
UUG
C
CUU
CUC
CUA
CUG
A
AUU
AUC
ile
AUA
AUG met (start)
ACU
ACC
ACA
ACG
G
GUU
GUC
GUA
GUG
GCU
GCC
GCA
GCG
phe
leu
leu
val
UCU
UCC
UCA
UCG
CCU
CCC
CCA
CCG
A
ser
UAU
UAC
UAA
UAG
pro
CAU
CAC
CAA
CAG
thr
AAU
AAC
AAA
AAG
ala
GAU
GAC
GAA
GAG
G
tyr
stop
stop
his
gln
asn
lys
asp
glu
UGU
UGC
UGA
UGG
CGU
CGC
CGA
CGG
AGU
AGC
AGA
AGG
GGU
GGC
GGA
GGG
cys
stop
trp
arg
ser
arg
gly
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
Third Base
First Base
U
mRNA codon chart
Alanine : Ala
Arganine: Arg
Asparagine: Asn
Aspartic acid: Asp
Cysteine: Cys
Glutamic acid: Glu
Glutamine: Gln
Glycine: Gly
Histidine: Hist
Isoleucine: Ile
Leucine: Leu
Lysine:Lys
Methionine: Met
Phenylalanine:Phe
Proline:Pro
Serine: Ser
Threonine: Thr
Tryptophan: Trp
Tyrosine:Tyr
Valine:Val
START: Met
Translation in a nutshell
Occurs in the cytoplasm
Requires a ribosome
Ribosomal complex= ribosome + mRNA+ tRNA
mRNA contains code for specific tRNA
Different tRNA’s bring different
amino acids to the ribosome
End result is a protein!
NUCLEUS
CYTOPLASM
(ribosome)
Central Dogma
DNA makes RNA makes Protein
• DNA  RNA = transcription
• RNA  Protein= translation
How do you go from DNA
to the color of your eyes?
3 genes
code for eye color
Transcription and
translation
Enzyme (protein)
That controls levels of
melanin
Mutations can change the meaning of
genes
• Mutations are changes in the DNA base
sequence
– caused by errors in DNA replication or by mutagens
– change of a single DNA nucleotide causes sickle-cell
disease
Normal hemoglobin DNA
mRNA
Mutant hemoglobin DNA
mRNA
Normal hemoglobin
Sickle-cell hemoglobin
Glu
Val
Figure 10.16A
• Types of mutations
NORMAL GENE
mRNA
Protein
Met
Lys
Phe
Gly
Ala
Lys
Phe
Ser
Ala
BASE SUBSTITUTION
Met
Missing
BASE DELETION
Met
Lys
Leu
Ala
His
Figure 10.16B
Types of Mutations
•
•
•
•
Missense (Substitution)
Nonsense (substitution)
Deletion (frameshift)
Insertion (frameshift)
•Chromosomal changes can be large or small
Deletion
Homologous
chromosomes
Duplication
Inversion
Reciprocal
translocation
Nonhomologous
chromosomes
Figure 8.23A, B