Notes

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NOTES: Chapter 13 - RNA & Protein
Synthesis
Vocabulary:
• Messenger RNA
(mRNA)
• Ribosomal RNA
(rRNA)
• Transfer RNA
(tRNA)
• Transcription
• RNA Polymerase
• Codon
• Translation
• Anticodon
Key Concepts:
•What are the 3 main types of
RNA?
What is transcription?
•What is translation?
1
Genes and Proteins:
• RECALL: the sequences of
nucleotides in DNA contain
INFORMATION!
• This information is put to
work through the production
of PROTEINS.
2
What do proteins do for the body?
• Proteins are diverse:
 control chemical messages in cell;
 direct the synthesis of carbo’s, lipids,
and nucleotides;
 enzymes;
 give the cell structure and
movement
• Goal of protein synthesis:
MAKE A PROTEIN
3
Protein Structure:
• RECALL: proteins are polymers of AMINO
ACIDS
• The sequence of nucleotides in each GENE
contains the information for the sequence of
AMINO ACIDS in a single protein
• Each human cell contains
about +/- 35,000 genes
4
•
•
•
•
Like DNA= made of nucleotides
copy of DNA segment
3 main types: mRNA, rRNA, tRNA
3 differences
1) sugar = ribose
2) single stranded
3) instead of the base thymine (T), RNA uses
URACIL (U)
5
6
Job of RNA: Function in
Protein Synthesis
7
Role of RNA – an analogy
•
Imagine what goes into a new car
being built on an automobile assembly
line:
1) Engineers make the design and tell
the workers how to make the cars;
2) Workers follow the directions to build
the cars;
3) Suppliers bring parts to the assembly
line so they can be installed in the car
8
Role of RNA – an analogy
•
Now imagine what goes into
PROTEIN SYNTHESIS:
1) DNA provides the “workers” with the
instructions for making proteins;
2) The workers (RNA molecules!) follow
the instructions from DNA and build
the proteins;
3) Other workers (other RNA molecules)
bring parts (AMINO ACIDS) over to
the assembly line
9
3 Types of RNA:
1) Messenger RNA (mRNA): brings
information from the DNA in the nucleus
out to the ribosomes;
2) Ribosomal RNA (rRNA): clamp on to the
mRNA and use its information to assemble
amino acids into a protein;
3) Transfer RNA (tRNA): the “supplier”;
transports amino acids to the ribosome
10
DNA  RNA
• How does the information in DNA ,
which is found in the nucleus, get out
to the ribosomes in the cytoplasm…it
needs a “MESSENGER”!
11
• Step #1 (of 2) of protein synthesis
• Transcribe: to make a copy
• transcribing DNA information (gene instructions)
into mRNA
– mRNA can leave the nucleus  ribosomes in the
cytoplasm
• special base sequences in DNA are recognized by
RNA as “start” and “stop” signals
– “Start” sequence called PROMOTER region of DNA
12
Details of the Process
• 1. RNA polymerase attaches to DNA at
the site where instructions for the needed
protein begins & it separates the 2 DNA
strands
13
2. RNA polymerase synthesizes the
mRNA strand using complementary
base-pairing
14
• Remember…there aren’t “T” bases in
RNA
• “C” binds with “G”
• DNA “A” binds with RNA “U”
15
Which strand was copied? A or B
16
3. when RNA polymerase reaches the end or
"STOP" part of the genetic code for that
protein, it releases
4. DNA re-zips
5. finished mRNA (message) leaves the
nucleus and goes to a ribosome in the
cytoplasm
17
• Bases are grouped by 3
• Called a CODON (“code”)
18
19
• Transcription ends with mRNA which
will exit the nucleus to the cytoplasm
• So… if transcription is the first step of
Protein Synthesis, what happens next in
the cytoplasm?
20
• Making a protein (string of amino acids):
translating from the language of nucleic
acids into a polypeptide
• How does it go from mRNA (copy of DNA) to
amino acids (building blocks of proteins)?
 A group of 3 mRNA bases makes up a
“codon” (think of as a “code word”)
 each codon specifies a particular amino
acid
 there are “start” and “stop” codons
21
1) mRNA attaches onto the ribosome
 3 nucleotides of mRNA = codon
• 2nd kind of RNA= ribosomal RNA (rRNA)
 makes up the majority of the ribosome
22
• 3rd kind of RNA= transfer RNA (tRNA)
 carries amino acids to the ribosomes (amino
acids join together)
 3 nucleotides of tRNA that “match” or
complement the mRNA = anticodon
 there are 64 different tRNA molecules
(more than 1 for each amino acid)
 REDUNDANCY of the CODE!!
23
Amino acid
24
amino acid
tRNA
anticodon
codon (mRNA)
25
2) By matching the codon of mRNA to the
anticodon of tRNA, the correct amino
acid is put into place
Next tRNA goes here!!!!
26
3) a peptide bond is formed between the
2 amino acids
27
4) protein chain continues to grow until a
“stop” codon is reached on the mRNA
 no tRNA exists for “stop” codons
28
Amino acid
· Molecules of tRNA are specific for
only 1 amino acid
-one end of tRNA attaches to
a
specific amino acid
-the other end attaches to mRNA
codon by base pairing
(anticodon = a sequence of 3 bases
on tRNA)
29
● tRNA’s decode the genetic
message codon by codon
30
31
This table shows
the “dictionary”
for the codons
and their
corresponding
amino acids
32
33
34
35
36
Translation: All At Once
37
PROTEIN SYNTHESIS: All At Once
38
PROTEIN SYNTHESIS
DNA
Step 1. TRANSCIPTION
(nucleus)
mRNA
Step 2. TRANSLATION
(ribosome)
tRNA
PROTEIN
39
40
Protein Synthesis—video
http://www.sciencenetlinks.com/interactives/protein.html
41
PRACTICE:
DNA: T A C C G C G G T T T A A C T
RNA:
amino
acids:
42
PRACTICE:
DNA: T A C C G C G G T T T A A C T
RNA: A U G G C G C C A A A U U G A
amino
acids:
43
PRACTICE:
DNA: T A C C G C G G T T T A A C T
RNA: A U G G C G C C A A A U U G A
amino
acids: met – ala - pro - asn - STOP
44
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