Protein Synthesis and Gene Expression Why does a cell need proteins to function properly? Time to make the proteins...

Protein Synthesis and Gene Expression

Why does a cell need proteins to function properly? Time to make the proteins...

SO…how does a cell make proteins anyway?

There are two important nucleic acids involved in making proteins... 1. DNA 2. RNA

Where are proteins made? B. Ribosomes

deoxyribonucleic acid zDNA: deoxyribonucleic acid double stranded. zDNA is double stranded. deoxyribose. zContains sugar deoxyribose. adenine, thymine, guanine, cytosine. zDNA contains bases adenine, thymine, guanine, cytosine. never zDNA never leaves the nucleus. ribonucleic acid zRNA: ribonucleic acid single stranded. zRNA is single stranded. ribose. zContains sugar ribose. adenine, guanine, cytosine and URACIL. zRNA contains bases adenine, guanine, cytosine and URACIL. can zRNA can leave the nucleus. Let’s Review DNA & RNA

Remember there are three types of RNA zmRNA: messenger RNA mRNA tRNA towing Amino acid zrRNA: ribosomal RNA ztRNA: transfer RNA. DNA Transcription Translation

Overall process of protein synthesis transcription translation DNA mRNA Protein

Summary of Protein Synthesis z DNA  mRNA  tRNA  protein 1.The process of going from DNA to mRNA is transcription. 2.The process of going from mRNA to protein is translation.

Let’s explore this in a little more detail... First, let’s see how the message in DNA gets to the ribosomes…

DNA’s tragedy zDNA contains volumes of information about making protein. zUnfortunately, DNA is too huge to leave the nucleus. If I could only get out there… I’d show them a thing or two! ribosomes nucleus

How does the cell solve this problem….transcription zThat’s where mRNA comes in. zmRNA helps get DNA’s message out to the ribosomes... How do I tell those guys what I want them to do? I can help!

First, DNA unzips itself... zDNA unzips itself, exposing free nitrogen bases.

IV. Transcription a.The process of going DNA to mRNA

IV. Transcription b. The steps of transcription: 1. First DNA unzips itself along the segment of code needed for a certain protein. 2. mRNA is made by forming complementary bases on the unzipped portion of DNA.

IV. Transcription DNA → RNA DNARNA A-T T-A G-C C-G AUGCAUGC

IV. Transcription b. The steps of transcription: 3. DNA’s code is copied into groups of 3 bases at a time called a codon. 4. Each codon codes for 1 amino acid. 5. Once the mRNA strand is transcribed, it can leave the nucleus to find a ribosome to carry out the next step.

Next, mRNA is made... zmRNA is made from the DNA template zmRNA matches with free DNA nitrogen bases in a complimentary fashion

Next, mRNA is made... zmRNA is made from the DNA template zmRNA matches with free DNA nitrogen bases in a complementary fashion

Some additional notes about making mRNA… zDNA contains two kinds of sequences: Coding and Noncoding regions

Some additional notes about making mRNA… zOne kind of noncoding is used to start transcription zAnother kind is call Introns and is old, unused sequences of bases zThe coding regions are called Exons zFinal Processed mRNA is made from Exons

mRNA leaves the nucleus... zDNA’s code is copied to mRNA in three letter groups called codons.  After mRNA is made from the DNA template, it is ready to leave the nucleus. I hope he can tell them what to do!

The next step... Translation

Translation

mRNA meets the Ribosomes! (No, it’s not a new sitcom on FOX…)

mRNA tries to talk to the ribosomes… zmRNA leaves the nucleus and travels to the cytoplasm, where the ribosomes are located. I have a message for you! It’s from DNA! What does he want now? It’s always something! Once there, mRNA meets up with the ribosomes

mRNA tries to talk to the ribosomes…but is unsuccessful. zHowever, the ribosomes cannot understand the message mRNA is carrying. Why don’t they get it??? @%$!! Why can’t we tell what he’s saying? We need a translator!

tRNA Saves the Day! Now the cell can make a protein! The boss will NOT be happy about this... We won’t work until we know what to do! Where is that translator? Looks like trouble for this cell… I’d better help! Tyrosine

tRNA: Transfer RNA Tyrosine 1.Chemically, tRNA is clover-leaf shaped. 2.At one end, it carries an amino acid (like a tow truck). 3.At the other end, it has a three letter code known as an anticodon.

Anticodon? What’s that? zThis anticodon is the complement to the codons contained within mRNA.  Can you find the mRNA complement to the anticodon on tRNA? Tyrosine

Some notes about Amino Acids zThere are 20 known amino acids present in living things. zHow is it possible to get a group of four letters to code for 20 things? zPut them into groups of three… y4 3 = 64 codes Number of nitrogen bases Number of members in a group of nitrogen bases

What’s a codon, anyway? zHere is what a codon looks like. It is a sequence of 3 bases. zHow we determine what amino acid each codon codes for must be read off of a codon chart. zThis is also known as the genetic code.

Codon chart UCA G U Phenylalanine Leucine Serine Tyrosine Stop Cysteine Stop Tryptophan UCAGUCAG C Leucine Proline Histidine Glutamine Arginine UCAGUCAG A Isoleucine Methionine Threonine Asparagine Lysine Serine Arginine UCAGUCAG G Valine Alanine Aspartic Acid Glutamic Acid Glycine UCAGUCAG First Base Second Base Third Base

Other Codon Charts

Reading a Codon Chart zIt is possible for some amino acids to have more than one codon. zThere are three stop codons…they are UAA, UGA and UAG. zThere is also one START codon…AUG.

How a Translator works… zFirst, the anticodons on tRNA meet up with the mRNA start codon (AUG) at the ribosome. zNext, another tRNA meets up with it’s corresponding mRNA. zEach tRNA carries an amino acid. Methionine

How a Translator works… zOnce two amino acids are made, a bond forms between them. zThis process continues until a stop codon on mRNA is reached. Methionine

Animation of translation Click to automatically start animation.

Single Messenger RNA Strand This is a ribosome.

Met Single Messenger RNA Strand

Met Single Messenger RNA Strand Ala

Single Messenger RNA Strand Met Ala

Single Messenger RNA Strand MetAlaPro

Single Messenger RNA Strand Met Ala Pro

Single Messenger RNA Strand Met Arg Pro

Single Messenger RNA Strand MetAlaPro

Single Messenger RNA Strand Met Ala Pro

Single Messenger RNA Strand Met Ala Pro Phe

Single Messenger RNA Strand Met Ala Gly Phe

Single Messenger RNA Strand Met Ala Pro Phe

Met Ala Pro Phe

MetAla Pro Phe Stop

MetAla Pro Phe

StopMetAla Pro Phe

How Does it Know When to Quit? zThis process continues until a stop or a termination codon (found on mRNA) is reached. zThere are three stop codons: UGA, UAA and UAG. STOP

Regulation of Transcription and Translation z Think about your house, do you keep all the lights on ALL the time in every room?? z Gene expression is a regulated process where genes can be turned on and off as needed due to environmental factors.

In summary… z DNA contains the information needed to make proteins. z However, DNA is too large to leave the nucleus. z RNA acts as a set of working instructions for ribosomes to make proteins. z This process is also known as gene expression. z Gene expression is a regulated process.

The Central Dogma is Universal

Protein Synthesis and Gene Expression Why does a cell need proteins to function properly? Time to make the proteins...

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Protein Synthesis and Gene Expression Why does a cell need proteins to function properly? Time to make the proteins...

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