Transcription and Translation

Transcription and Translation

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

Genes and Proteins • Proteins become structures such as filaments in muscle tissue, and enzymes that control chemical reactions • DNA (sequences of nucleotides) contains information that is used in the production of proteins

SO…How does a cell make proteins anyway?

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, guanine, cytosine, and thymine. 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

transcription translation Overall process of protein synthesis DNA RNA Protein translation transcription Occurs in the nucleus Occurs in the cytoplasm

Remember that the monomer for proteins is amino acids!

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 information about making proteins. • DNA is found in the nucleus. • Ribosomes make proteins. • Unfortunately, DNA is unable to leave the nucleus. • That’s where mRNA comes in… ribosomes nucleus

How does the cell solve this problem?….Transcription How do I tell those guys what I want them to do? • DNA is transcribed into a copy of mRNA, which can leave the nucleus. • 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 TACTGCTAA First, DNA unzips itself... • When DNA unzips itself (exposing free nitrogen bases)…

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

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

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

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

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

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

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

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

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

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

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.

Transcription- Review • Process in which enzymes create an RNA copy of a portion of the DNA molecule • Enzymes unzip DNA as in replication • Free RNA nucleotides pair with one of the DNA strands • When process is completed, the mRNA molecule breaks away and the DNA strands rejoin; mRNA leaves the nucleus and enters the cytoplasm

AUGUGCUAA The next step...Translation mRNA meets the Ribosomes!

I have a message for you! It’s from DNA! AUGUGCUAA 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? The mRNA instructions are written as a series of 3-nucleotide sequences, called codons

Why don’t they get it??? @%$!! AUGUGCUAA 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.

Methionine AUGUGCUAA UAC 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. • At the other end, it has a three letter code known as an anticodon. Methionine UAC

AUGUGCUAA Anticodon? What’s that? Methionine • This anticodon on tRNA is complementary to the codons on mRNA. • Can you find the mRNA complement to the anticodon on tRNA? UAC

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? • A codon 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.

Codon Chart Third letter

Methionine AUGUGCAGG UAC 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.

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

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

AUGUGCAGG Here’s the process…animated!

Transcription and Translation