TranscriptionUnit 4 Part I

Central Dogma

DNARNA Proteins Traits

This is the central theme of molecular genetics.

These are the steps needed to get from a DNA double helix to your blue eyes.

Central Dogma

How do you get from DNA to RNA to Proteins to Traits?

DNA RNA PROTEINS TRAITS Transcription Translation control into Amino Acids

Review

DNA can be found in the nucleus.

Ribosomes make proteins and are found in the cytoplasm.

How does DNA (which doesn’t leave the nucleus) get to the ribosomes in the cytoplasm? It becomes mRNA

and leaves through the nuclear pores.

DNA vs. RNA

DNA

Deoxyribonucleic Acid Deoxyribose sugar Double stranded N bases = A,T,C,G Found in the nucleus 1 type Contains a nucleotide

= phosphate + sugar + N base

RNA

Ribonucleic Acid Ribose sugar Single stranded N bases = A,U,C,G

Uracil replaces Thymine Found in the nucleus and

cytoplasm 3 types: mRNA, tRNA &

rRNA Contains a nucleotide =

phosphate + sugar + N base.

DNA vs. RNA

DNA RNA

Types of RNA Messenger RNA

mRNA Carries info from DNA and

delivers it to ribosome – codon.

Ribosomal RNA rRNA Structural component of

ribosomes Translates mRNA sequences

and signals tRNA Transfer RNA

tRNA Transfers the correct amino

acid for the protein – anticodon.

How does the DNA become mRNA?

Through a process called Transcription. Steps:

RNA Polymerase binds to a region of DNA that signals it to start making RNA.

RNA Polymerase unwinds and unzips the gene segment on DNA.

One strand of DNA acts as a template for making mRNA.

Enzyme moves along the DNA bases in one direction. It reads each nucleotide and pairs it with a complementary RNA nucleotide.

Process continues until enzyme reaches a terminator (stop signal.)

Enzyme detaches from DNA and releases mRNA from the nucleus.

DNA - RNA

What would the mRNA strand be if the DNA template is: (remember that A now pairs with U

and C still pairs with G)

ATC CAG TCA GAT CTA CCG TGA CTG GGA

Transcription Review DNA makes proteins, which control all of our

traits, but DNA cannot leave the nucleus. So to get it’s message to the protein factories

(ribosomes) in the cytoplasm. It makes mRNA.

The enzyme, RNA polymerase exposes a DNA template and adds one RNA nucleotide at a time to make an mRNA molecule.

Transcription Review cntd. Eventually RNA polymerase will reach a

spot on the DNA that signals it to stop making the mRNA strand.

After it reaches this point it can let go and leave the nucleus.

From the nucleus it goes into the cytoplasm and attaches to a ribosome.

Translation at the ribosome

Step where the mRNA code is translated into an amino acid sequence – a protein. A series of amino acids held together by

peptide bonds. 20 amino acids – 8 essential a.a.’s - meaning

your body cannot make them you must consume them from food.

Translation @ ribosome w/mRNA & tRNA

RNA is read 3 nitrogen bases at a time Each triplet of bases is called a codon

Each 3 letter codon is a code for an amino acid

A series of 50-5,000 amino acids make up a protein.

Translation/Protein Synthesis Steps

Once the mRNA codon sequence leaves the nucleus it attaches to the ribosome.

The ribosome (which is partly made up of an rRNA molecule) travels down the mRNA sequence until it finds a start spot called a start codon There is only 1 start codon AUG --- it codes for the amino acid,

Methionine. The start codon is the spot where the amino

acids start to make proteins.

Translation/Protein Synthesis Steps

After the ribosome finds the start codon a transfer RNA molecule (tRNA) attaches to the codon by an anti-codon and brings an amino acid to the ribosome. The tRNA anticodon carries the amino acid.

Amino acids are deposited onto the mRNA strand until it reaches one of 3 stop codons. UAA, UAG, UGA

After a stop codon is reached the animo acid chain is let go and folded and modified into a protein.

Translation/Protein Synthesis

How does the tRNA molecule know what amino acid to drop off? Anti-codon of tRNA must match codon of

mRNA.

Each codon codes for a particular amino acid being carried by the tRNA anticodon.

To determine what amino acid matches which codon refer to the codon chart.

DNA vs. RNA Review

DEOXYRIBONUCLEIC ACID

DNA Double stranded Made up of repeating

units called nucleotides. Contains the 5 C

(pentose) sugar Deoxyribose.

Found in the nucleus 4 nitrogen bases

Adenine, Guanine, Cytosine, Thymine

RIBONUCLEIC ACID

RNA Single Stranded Made up of repeating units

called nucleotides. Contains the 5 C sugar

ribose. Found in the nucleus &

cytoplasm 4 nitrogen bases

Adenine, Guanine, Cytosine, uracil

3 forms mRNA, rRNA, tRNA