PROTEIN SYNTHESIS• It is known today that GENES direct the

production of the proteins that determine the phonotypical characteristics of organisms.

» GENES = a sequence of nucleotides in DNA that performs a specific function such as coding for a particular protein

Wednesday, July 13, 2011

PROTEIN SYNTHESIS• The CENTRAL DOGMA of molecular genetics is the

sequence whereby DNA is transcribed into a complementary RNA message that is capable of leaving the nucleus and delivering it to the ribosomes. The ribosomes then translate the message into polypeptide chains which are processed into proteins.

DNA transcription mRNA translation polypeptide chain protein

Wednesday, July 13, 2011

CENTRAL DOGMA

Transcription = occurs in the nucleus involves the copying of the information in DNA into messenger RNA (mRNA).

Translation = occurs in the cytoplasm involves ribosomes using the mRNA as a blueprint to synthesize a protein composed of amino acids.

Wednesday, July 13, 2011

RIBONUCLEIC ACID (RNA)• RNA differs from DNA in many ways:

» RNA contains a ribose sugar rather than a deoxyribose sugar

» Instead of thymine, RNA contains the base URACIL

» RNA is single stranded (whereas DNA is double)

When a gene is transcribed into mRNA, only a single-stranded

complementary copy is made. In this copy, uracil is substituted for

thymine.

Wednesday, July 13, 2011

RIBONUCLEIC ACID (RNA)• There are 3 major classes of RNA

molecules:» messenger RNA (mRNA) – the end product of

transcription of a gene, mRNA is translated by ribosomes into protein

» transfer RNA (tRNA) – a form of RNA that is responsible for delivering amino acids to the ribosomes during the process of translation

» ribosomal RNA (rRNA) – a form of RNA that binds with ribosomal protein to form ribosomes

*see table on pg. 239*

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• There are 20 amino acids found in proteins and only 4 different bases in mRNA.

• To code for all 20 amino acids, a sequence of 3 nucleotides must be used for each amino acid.

• Each triplet of nucleotides is called a CODON

GENETIC CODE

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GENETIC CODE

This leads to a total of 64 codons which can code for any of the 20 amino acids.

More than one codon can code for the same amino acid. This redundancy helps to minimize possible mutations.

START CODON

= AUG – signals that translation commences at that point.

STOP CODON

= UGA, UAA, UAG – signals that translation terminates at that point.

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TRANSCRIPTION• Transcription occurs in the nucleus and is the

process whereby DNA is transcribed into mRNA.

• This process occurs in 3 main phases:» INITIATION» ELONGATION» TERMINATION

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TRANSCRIPTION• http://www.youtube.com/watch?

v=ztPkv7wc3yU

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TRANSLATION• once transcribed, mRNA then exits the

nucleus!

• once it enters the cytoplasm, it is ready to be translated

» by RIBOSOMES!!!!!!!

Ribosomes bind to the mRNA at the 5`cap – this signals the initiation of translation!

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TRANSLATION• In translation, the ribosome moves along the

mRNA in the 5`-to-3`direction adding a new amino acid to the growing polypeptide chain every time it reads a new codon.

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READING FRAME• The phase in which mRNA is read, in triplets

of nucleotides is known as the READING FRAME.

» the reading frame can differ depending on the base pair that the ribosome starts reading

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Role of tRNA• Ribosomes alone do not synthesize the

protein.

• tRNA is needed to deliver the appropriate amino acid to the polypeptide building site.

tRNA is a single stranded nucleic acid whose structure resembles that of a clover leaf.

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Role of tRNAANTICODON = group of 3 complementary bases on tRNA that recognizes and pairs with a codon on the mRNA.

Every specific tRNA carries only one specific amino acid.

Since there are 20 different amino acids and there are 64 different codons, there are between 20 and 64 possible tRNA molecules!!!!

Wednesday, July 13, 2011

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

• http://www.youtube.com/watch?v=B6O6uRb1D38&feature=related

• http://www.youtube.com/watch?v=D5vH4Q_tAkY&feature=related

• http://www.youtube.com/watch?v=5bLEDd-PSTQ&feature=related

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MUTATIONS• http://www.youtube.com/watch?

v=kp0esidDr-c

• http://www.youtube.com/watch?v=vNWwSL55gUM&feature=related

Wednesday, July 13, 2011