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RNA and Protein Synthesis
Gene
• Segment of DNA that specifies the sequence
of amino acids in protein
RNA structure
1. Single stranded
2. Ribose replaces
deoxyribose
3. Uracil replaces thymine
Uracil instead
of thymine
Main function of RNA
• Protein synthesis
Amino acid sequence
20 different amino acids
journal
• Information, Please
• DNA contains the information
that a cell needs to carry out
all of its functions. In a way,
DNA is like the cell’s
encyclopedia. Suppose that
you go to the library to do
research for a science project.
You find the information in an
encyclopedia. You go to the
desk to sign out the book, but
the librarian informs you that
this book is for reference only
and may not be taken out.
1.
Why do you think the library
holds some books for
reference only?
2.
If you can’t borrow a book,
how can you take home the
information in it?
3. All of the parts of a cell are
controlled by the information
in DNA, yet DNA does not
leave the nucleus. How do you
think the information in DNA
might get from the nucleus to
the rest of the cell?
Location of protein synthesis
ribosomes
3 types of RNA
• Messenger RNA (mRNA)
– Takes message from DNA in nucleus to ribosomes in
cytoplasm
• Contains codons
• DNA strand: A T C G A T C T T A A T C
• m RNA strand: U A G C U A G
codon
codon
• Ribosomal RNA (rRNA)
– Found in ribosomes along with other proteins
• Transfer RNA (tRNA)
– Transfers each amino acid to the ribosome
• Contains anitcodons (complementary to codon)
Protein synthesis happens in 2 steps:
1. Transcription: RNA copies DNA sequence (but U for T)
RNA polymerase
Separates DNA and builds complementary RNA strand
Occurs in nucleus, then edited and mRNA copy moves to cytoplasm
Promoter
Tell mRNA where gene starts
2. Translation: mRNA directs sequence of amino acids
- Assembles protein based on info from mRNA
- tRNA brings specific amino acids to chain
- anticodon of the tRNA complements the codon of the mRNA
TRANSCRIPTION
Messenger RNA
RNA
polymerase
DNA
RNA
mRNA has to be edited before leaves nucleus
introns get removed
Introns don’t code for proteins
- so removed
Exons
- do code for proteins
“Genetic Code” is on mRNA
Instructs sequence of amino acids
AUCG :letters make up code
Triplet code: 3 nucleotide bases = one codon
- Each codon encodes for one amino acid (except
“stop” codons)
- There are codons for all 20 different amino acids
Start codon
AUG
Translation
Stop codons
UGA, UAA, UAG
anticodon
Chapter 12
Chapter 12
RNA
can be
Messenger RNA
also called
Ribosomal RNA
which functions to
mRNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
tRNA
Bring
amino acids to
ribosome
Regulation of Protein Synthesis
Every cell in your body, with the exception of gametes, or
sex cells, contains a complete copy of your DNA. Why, then,
are some cells nerve cells with dendrites and axons, while
others are red blood cells that have lost their nuclei and are
packed with hemoglobin? Why are cells so different in
structure and function? If the characteristics of a cell
depend upon the proteins that are synthesized, what does
this tell you about protein synthesis? Work with a partner to
discuss and answer the questions that follow.
1. Do you think that cells produce all the proteins for
which the DNA (genes) code? Why or why not? How
do the proteins made affect the type and function of
cells?
Practice on board
Practice on board:
Then complete HW
Mutations start here
What can mutations do to amino acid
sequence?
• 1. Copy the following information about Protein X: Methionine—
Phenylalanine—Tryptophan—Asparagine—Isoleucine—STOP.
• 2. Use Figure 12–17 on page 303 in your textbook to determine
one possible sequence of RNA to code for this information. Write
this code below the description of Protein X. Below this, write the
DNA code that would produce this RNA sequence.
• 3. Now, cause a mutation in the gene sequence that you just
determined by deleting the fourth base in the DNA sequence. Write
this new sequence.
• 4. Write the new RNA sequence that would be produced. Below
that, write the amino acid sequence that would result from this
mutation in your gene. Call this Protein Y.
• 5. Did this single deletion cause much change in your protein?
Explain your answer.
Substitution
Insertion
Deletion
Deletion
Duplication
Inversion
Translocation
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