PROTEIN SYNTHESIS

Why are proteins important?

• proteins help build cell structures

• some proteins are enzymes that promote biological reactions

• Proteins are found in muscles, blood, bones, etc..

RNA

RNA is an important mechanism

of protein synthesis

DNA review

Deoxyribonucleic acid

• Contains the sugar deoxyribose

• Adenine pairs with Thymine

• Cytosine pairs with Guanine

• Double stranded (double helix shape)

RNA

Ribonucleic acid

• Contains the sugar ribose

• Uracil substitutes Thymine

• Adenine pairs with Uracil

• Single stranded

RNA makes a complimentary copy of one side of the DNA double helix

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

RNA: A U G C U A G C G U C A C G U A C U U A A

3 types of RNA

mRNA: messenger RNA

tRNA: transfer RNA

rRNA: ribosomal RNA

messenger RNA

• transcribes a portion of genetic code from DNA (gene)

• Transfers genetic code from the nucleus to the cytoplasm

• Contains codons: nirogen bases that occur in 3- letter groups

Think: Why must DNA be copied onto RNA?

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=l86ZheY7P7LWwM&tbnid=StdVum3qL2Bc5M:&ved=0CAUQjRw&url=http://www.yalescientific.org/2013/04/a-genetic-light-switch-riboswitches-shed-light-on-the-history-of-life/2-mrna-formation-crescentok-com/&ei=FdHVUdjaKIL49QTN3oGIAQ&psig=AFQjCNHEjlPMB5gqzip1h9mlq5dHeHqZYw&ust=1373053540209229

transfer RNA

• Translates the message by transferring amino acids from the cytoplasm to the ribosome

• Contains anti-codons that complement mRNA codons

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=5fRTR5rlmzu2bM&tbnid=5rE3-z_YJibJtM:&ved=0CAUQjRw&url=http://droualb.faculty.mjc.edu/Course Materials/Physiology 101/Chapter Notes/Fall 2011/chapter_2 Fall 2011.htm&ei=jNLVUfnMFYbq8gTsrYCIDg&psig=AFQjCNHPZc8ZZPt7bItEmcm7VDTw7WRbtg&ust=1373053859967922

ribosomal RNA

• Structural component of ribosome that binds mRNA and tRNA together

• Makes up 80% of all RNA in the cell

Review:

What is the function of a ribosome? (cell structure)

Synthesizes proteins What are the monomers that make up a protein? (biochemistry)

Amino acids

Think:

A ribosome synthesizes proteins by linking amino acids together and folding them into a 3-dimensional shape.

HOW does the ribosome know which amino acids to link together, in what sequence, and in what shape?

The nitrogen base sequence of the RNA is the genetic instructions!

RNA are the instructions

The ribosome assembles the protein

Label the diagram below using the following terms:

DNA, mRNA, tRNA, amino acid

3

4

PROTEIN SYNTHESIS

Proteins are synthesized through two major processes

• Transcription

• Translation

TRANSCRIPTION

1. A segment of the DNA double helix (gene) is unzipped

2. The RNA polymerase enzyme adds complimentary mRNA nucleotides to one strand of the DNA

Practice:

Determine the complimentary mRNA sequence

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

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

• The nitrogen base sequence in mRNA is the genetic instructions for building a protein

• mRNA nitrogen bases occur in 3 letter groups called codons

• Each codon corresponds to a specific amino acid

Practice:

Separate the mRNA sequence into codons

A U G C U A G C G U C A C G U A C U U A A

A U G – C U A – G C G – U C A – C G U – A C U – U A A

3. The new mRNA strand leaves the nucleus and enters the cytoplam where ribosomes are found

• DNA winds back up and stays in the nucleus

Think:

Why must DNA be copied onto RNA?

• DNA cannot leave the nucleus

• Ribosomes (the site of protein synthesis) are located in the cytoplasm

TRANSLATION

4. mRNA attaches to a ribosome in the cytoplasm

5. tRNA translates the codons of mRNA and retreives the corresponding amino acids from the cytoplasm

Remember:

• Each mRNA codon correspond to a specific amino acid

• Each tRNA molecule contains a complimentary anti-codon sequence

• This is how tRNA knows which amino acid to retrieve

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=Ci0K_yldtqCeLM&tbnid=9ScguMOwaMB_7M:&ved=0CAUQjRw&url=http://youngbloodbiology.wikispaces.com/Process+of+Translation&ei=L8nVUZvtFoq48wSYoIHoDA&psig=AFQjCNE4IfWd16_aGQ2EaC0oDuws2w_w4Q&ust=1373046829783766

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=D94NHjC4OVcKLM&tbnid=wl30-S37EkYIGM:&ved=0CAUQjRw&url=http://community.iisme.org/lessons/display.cfm?lessonid=865&fileid=5197&ei=xMnVUa_xCo6w8QTelIDgDw&psig=AFQjCNFp_7KAUTZr_VZ_4nw8K4pnRrZ6OQ&ust=1373051696379047

6. The ribosome assembles the amino acids delivered by tRNA into a polypeptide chain

Practice: Transcribe, then translate the original DNA sequence into an polypeptide chain. (Use the codon chart to find the amino acids) DNA (gene): T A C G A T C G C A G T G C A T G A A T T

TRANSCRIPTION

mRNA (codons): AUG - CUA – GCG – UCA – CGU – ACU – UAA

TRANSLATION

tRNA (anticodons): UAC - GAU - CGC - AGU - GCA - UGA – AUU amino acid sequence (polypeptide chain): INITIATION (START) - LEUCINE – ALANINE – SERINE – ARGININE – THREONINE - STOP

Why do some amino acids correspond to more than one codon?

4 nitrogen bases: A U C G

1 codon = 3 bases

43 = 64 possible codon sequences

There are only 20 amino acids, so some have more than one code

7. The polypeptide chain is folded into a specific 3-dimensional shape

VIOLA! We have a protein.

What determines the type of protein being made?

• The sequence of amino acids

• The shape the polypeptide chain is folded into

?

Review: fill in the blank

?

Protein synthesis animations

http://www.youtube.com/watch?v=Ikq9AcBcohA

http://www.youtube.com/watch?v=NJxobgkPEAo