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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?

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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 +/- 35,000 genes

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• Like DNA= made of nucleotides• copy of DNA segment• 3 main types: mRNA, rRNA, tRNA• 3 differences

1) sugar = ribose2) 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 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

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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 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

complement 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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This table 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

RNA:

amino

acids:

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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:

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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