Warm Up

Warm Up The genetic code of a DNA molecule is determined by a specific sequence of A. ATP molecules C. chemical bonds B. sugar molecules D. nitrogenous bases

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

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

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

Overall process of protein synthesis transcription translation mRNA DNA Protein

Summary of Protein Synthesis • DNA  mRNA  tRNA  protein • The process of going from DNA to mRNA is transcription. • 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 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.

IV. Transcription • 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 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.

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 complementary 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, tRNA is clover-leaf shaped. • At one end, it carries an amino acid (like a tow truck). • 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

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