Protein Synthesis – Protein Synthesis – ReviewReview

Review!!Review!!

http://learn.genetics.utah.edu/http://learn.genetics.utah.edu/content/begin/tour/content/begin/tour/

An Overview…An Overview…

Genes on chromosomes need to be Genes on chromosomes need to be transcribedtranscribed into RNA, and then into RNA, and then translatedtranslated by ribosomes into protein. by ribosomes into protein.

Genes act by directing the production of Genes act by directing the production of only ONE protein each. only ONE protein each. • This is known as the one gene-one enzyme This is known as the one gene-one enzyme

hypothesis.hypothesis. An error in gene sequence can result in a An error in gene sequence can result in a

change in protein sequence, shape, and change in protein sequence, shape, and therefore function. therefore function. • TRY THIS: Activity p 233, Translating the Code.TRY THIS: Activity p 233, Translating the Code.

Overview…Overview…

DNA in the nucleus is TRANSCRIBED DNA in the nucleus is TRANSCRIBED into a into a complementary RNA complementary RNA messagemessage that moves to the that moves to the cytoplasm. (copied from one cytoplasm. (copied from one medium to another)… medium to another)…

Numerous RNA copies can move to Numerous RNA copies can move to different ribosomes. different ribosomes.

OverviewOverview

The ribosomes TRANSLATE the message The ribosomes TRANSLATE the message into into Polypeptide chainsPolypeptide chains and process into and process into proteins (convert into a different proteins (convert into a different language).language).

TranscriptionTranscription involves the copying of involves the copying of information in DNA into mRNAinformation in DNA into mRNA

TranslationTranslation involves ribosomes using involves ribosomes using mRNA as blueprint to synthesize a protein mRNA as blueprint to synthesize a protein composed of amino acids.composed of amino acids.

A Cool VisualA Cool Visual

http://www.youtube.com/watch?http://www.youtube.com/watch?v=41_Ne5mS2lsv=41_Ne5mS2ls

RNARNA

ribose sugar with a ribose sugar with a hydroxyl on hydroxyl on 2’ 2’ CarbonCarbon

uracil replaces the uracil replaces the base thymine and base thymine and pairs with adeninepairs with adenine

single strandedsingle stranded

3 Types of RNA3 Types of RNA

Messenger RNAMessenger RNA (mRNA): varies in (mRNA): varies in length, end product of transcription length, end product of transcription of a gene, moves to the ribosomeof a gene, moves to the ribosome

Transfer RNATransfer RNA (tRNA): delivers (tRNA): delivers amino acids to the ribosomes for amino acids to the ribosomes for translation. Shaped like a translation. Shaped like a cloverleaf; very short.cloverleaf; very short.

Ribosomal RNARibosomal RNA (rRNA): binds with (rRNA): binds with protein to make ribosomesprotein to make ribosomes

Step 1 - TranscriptionStep 1 - Transcription

Within the nucleus, theWithin the nucleus, the

DNA of a particular DNA of a particular genegene

unwinds and separates.unwinds and separates.

One strand of the DNA isOne strand of the DNA is

transcribed intotranscribed into

messenger RNA (mRNA)messenger RNA (mRNA)

in a process calledin a process called

transcriptiontranscription..

Transcription – Making mRNATranscription – Making mRNA

Transcription divided into three Transcription divided into three sequential processes…sequential processes…

• InitiationInitiation RNA polymerase bindsRNA polymerase binds to DNAto DNA at specific at specific

site known as site known as promoterpromoter, near the beginning , near the beginning of the gene. (usually high [] of A & T…only 2 of the gene. (usually high [] of A & T…only 2 bonds to break!)bonds to break!)

• ElongationElongation Enzyme Enzyme RNA polymeraseRNA polymerase puts together puts together

the appropriate ribonucleotides and the appropriate ribonucleotides and builds builds the mRNA transcriptthe mRNA transcript

• TerminationTermination Shortly after RNA polymerase passes the Shortly after RNA polymerase passes the

end of a gene, recognizes signal to stop end of a gene, recognizes signal to stop transcribingtranscribing

mRNA transcript then is completely released mRNA transcript then is completely released from the DNA and will exit the nucleusfrom the DNA and will exit the nucleus

http://www.youtube.com/watch?http://www.youtube.com/watch?v=ztPkv7wc3yUv=ztPkv7wc3yU

The Final Touches…The Final Touches… the mRNA must be prepared to leave the the mRNA must be prepared to leave the

nucleus. A 5’ cap is added (for nucleus. A 5’ cap is added (for protection), and a poly A tail is added to protection), and a poly A tail is added to the 3’ endthe 3’ end

The mRNA contains regions of code that The mRNA contains regions of code that do not make the protein (introns). do not make the protein (introns). Introns are removed by spliceosomes.Introns are removed by spliceosomes.

Spliceosomes join exons (coding regions) Spliceosomes join exons (coding regions) together. together.

The mRNA strand leaves the nucleus and The mRNA strand leaves the nucleus and binds with ribosomes in the cytoplasm. binds with ribosomes in the cytoplasm.

P 249, Q 1-6P 249, Q 1-6

Step 2 TranslationStep 2 Translation Once mRNA enters Once mRNA enters

cytoplasm, it is ready to be cytoplasm, it is ready to be translationtranslation

Ribosomes: made up of two Ribosomes: made up of two parts: a large subunit (60s) parts: a large subunit (60s) and a small subunit (40s). and a small subunit (40s). Bind to the mRNA Bind to the mRNA (recognizing the 5’ cap)(recognizing the 5’ cap)

Must be lined up correctly to Must be lined up correctly to the proper reading frame the proper reading frame (reading triplets correctly)(reading triplets correctly)

tRNAtRNA

tRNA delivers amino acids to the polypeptide building tRNA delivers amino acids to the polypeptide building site (ribosome)site (ribosome)

tRNA is a small single stranded nucleic acid, tRNA is a small single stranded nucleic acid, resembles a cloverleafresembles a cloverleaf

one arm: anticodon (sequence of three bases one arm: anticodon (sequence of three bases complementary to mRNA)complementary to mRNA)

3’ end has acceptor site for a particular amino acid3’ end has acceptor site for a particular amino acid• this recognition by tRNA of mRNA is facilitated this recognition by tRNA of mRNA is facilitated

through complimentary base pairing.through complimentary base pairing. every tRNA carries only one specific amino acid every tRNA carries only one specific amino acid

• therefore there must be at least 20 (20-64) therefore there must be at least 20 (20-64) different tRNA’sdifferent tRNA’s

TranslationTranslation

TranslationTranslation2.2. The mRNA consists of The mRNA consists of nucleotides nucleotides that code for a that code for a

specific amino acid. The code is in triplet called a CODON specific amino acid. The code is in triplet called a CODON (3 nucleotides = 1 amino acid). Amino acids are brought (3 nucleotides = 1 amino acid). Amino acids are brought into place by a molecule known as transfer RNA (tRNA). into place by a molecule known as transfer RNA (tRNA). This process is known as This process is known as translationtranslation. Peptide bonds . Peptide bonds occur b/w amino acids.occur b/w amino acids.

Building the Chain…Building the Chain… First codon recognized is start (AUG-First codon recognized is start (AUG-

methionine)- aligns the reading framemethionine)- aligns the reading frame ribosome contains two sites for tRNA: ribosome contains two sites for tRNA:

an A (acceptor) site and a P (peptide) an A (acceptor) site and a P (peptide) site. site.

tRNA (Met- AUG) enters the P site. tRNA (Met- AUG) enters the P site. the rest of the tRNA enter at the A site the rest of the tRNA enter at the A site

and form peptide bonds between the and form peptide bonds between the amino acids as the chain forms. amino acids as the chain forms.

Ribosome translocates one codon over Ribosome translocates one codon over and continues the chain until it reaches a and continues the chain until it reaches a stop codon. (UGA, UAG, UAA)stop codon. (UGA, UAG, UAA)

A release factor protein dismantles the A release factor protein dismantles the complex, releasing the polypeptide chain.complex, releasing the polypeptide chain.

Enzymes may cleave the chain at specific Enzymes may cleave the chain at specific places places

http://www.youtube.com/user/ndsuvirtualcell#p/a/44B161B3F290FC23/0/5bLEDd-PSTQ

Protein Synthesis Protein Synthesis

Once all the triplet codes (Codons) Once all the triplet codes (Codons) are read and the amino acids are are read and the amino acids are brought into place, the completed brought into place, the completed protein travels through the ER to protein travels through the ER to the Golgi.the Golgi.

The Golgi modifies the structure The Golgi modifies the structure and packages it into a vesicle.and packages it into a vesicle.

Vesicle moves to the membrane Vesicle moves to the membrane and is released by exocytosis.and is released by exocytosis.

More Homework...More Homework... P 241 Q1-9P 241 Q1-9 P 254 Q1-4P 254 Q1-4