Protein Synthesis and Gene Expression

Protein Synthesis and Gene Expression

Why does a cell need proteins to function properly? Time to make the proteins... Proteins are important molecules in our body because some serve as enzymes, hormones, and provide structure (muscles, hair, cartilage).

SO…how does a cell make proteins anyway? Transcription and Translation

There are two important nucleic acids involved in this process... DNA RNA

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

mRNA Amino acid tRNA towing Remember there are three types of RNA • mRNA: messenger RNA • tRNA: transfer RNA. • rRNA: ribosomal RNA

Overall process of protein synthesis transcription translation DNA RNA Protein

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

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

ATGACGATT TACTGCTAA First, DNA unzips itself... • DNA unzips itself, exposing free nitrogen bases.

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

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

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

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

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

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

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

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

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

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

Some additional notes about making mRNA… • DNA contains many non-coding regions, also known as “junk DNA” • RNA is not made from the junk DNA

UACUGCUAA mRNA leaves the nucleus... I hope he can tell them what to do! • DNA’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.

UACUGCUAA The next step...Translation mRNA meets the Ribosomes! (No, it’s not a new sitcom on Fox…)

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

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

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

tRNA: Transfer RNA • Chemically, tRNAis clover-leaf shaped. • At one end, it carries an amino acid. • At the other end, it has a three letter code known as an anticodon. Tyrosine AUG

UACUGCUAA Anticodon? What’s that? Tyrosine • This anticodon is the complement to the codons contained within mRNA. • Can you find the mRNA complement to the anticodon on tRNA? AUG

Some notes about Amino Acids • There are 20 known amino acids present in living things. • How is it possible to get a group of four letters to code for 20 things? • Put them into groups of three… • 43 = 64 codes Number of members in a group of nitrogen bases Number of nitrogen bases

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

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

The Wonderful World of Amino Acids • It is possible for some amino acids to have more than one codon. • There are three stop codons…they are UAA, UGA and UAG. • There is also one START codon…AUG.

Tyrosine UACUGCUAA AUG How a Translator works… • First, the anticodons on tRNA meet up with the mRNA start codon (AUG) at the ribosome • Next, another tRNA meets up with it’s corresponding mRNA. • Each tRNA carries an amino acid. Ribosome

Tyrosine UACUGCUAA AUG How a Translator works… Ribosome • Once two amino acids are made, a bond forms between them • This process continues until a stop codon on mRNA is reached.

UACUGCUAA Here’s the process…animated! Note: this is a really basic representation of this process!

UACUGCUAA Here’s the process…animated!

UACUGCUAA AUG tyrosine Here’s the process…animated!

Protein Synthesis and Gene Expression