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NOTES: 13.1-13.2 -

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?

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Genes and Proteins:• RECALL: the sequences of

nucleotides in DNA contain INFORMATION!

• This information is put to work through the production of PROTEINS.

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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

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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 20-30,000 genes

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• 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)

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Job of RNA: Function in Protein Synthesis

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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

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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

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3 Types of RNA:

1) Messenger RNA (mRNA): brings information from the DNA in the nucleusout 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

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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”!

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• Step #1 (of 2) of protein synthesis

• Transcribe: to make a copy

• transcribing DNA information (gene instructions) into mRNA

– mRNA can leave the nucleus goes to 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

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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

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2. RNA polymerase synthesizes the mRNA strand using complementary base-pairing

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• Remember…there aren’t “T” bases in RNA

• “C” binds with “G”

• DNA “A” binds with RNA “U”

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Which strand was copied? A or B

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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

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• Bases are grouped by 3

• Called a CODON (“code”)

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• 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?

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• 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

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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

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• 3rd kind of RNA= transfer RNA (tRNA)

carries amino acids to the ribosomes (amino

acids join together)

3 nucleotides of tRNA that “match” or

compliment the mRNA = anticodon

there are 64 different tRNA molecules

(more than 1 for each amino acid)

REDUNDANCY of the CODE!!

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Amino acid

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amino acid

tRNA

anticodon

codon (mRNA)

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2) By matching the codon of mRNA to the anticodon of tRNA, the correct amino acid is put into place

Next tRNA goes here!!!!

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3) a peptide bond is formed between the 2 amino acids

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4) protein chain continues to grow until a “stop” codon is reached on the mRNA

no tRNA exists for “stop” codons

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● 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)

Amino acid

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● tRNA’s decode the genetic

message codon by codon

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**table 13.6 on

page 367 shows

the “dictionary”

for the codons

and their

corresponding

amino acids

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Translation: All At Once

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PROTEIN SYNTHESIS: All At Once

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PROTEIN SYNTHESIS

Step 1. TRANSCIPTION

(nucleus)

Step 2. TRANSLATION

(ribosome)

DNA

mRNA

tRNA

PROTEIN

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Protein Synthesis—video

http://www.sciencenetlinks.com/interactives/protein.html

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PRACTICE:

DNA: T A C C G C G G T T T A A C T

mRNA:

amino

acids:

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PRACTICE:

DNA: T A C C G C G G T T T A A C T

mRNA: A U G G C G C C A A A U U G A

amino

acids:

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PRACTICE:

DNA: T A C C G C G G T T T A A C T

mRNA: A U G G C G C C A A A U U G A

amino

acids: met – ala - pro - asn - STOP