The Making of a Protein!

Transcription

DNA holds the instructions

When proteins are produced in the body, the instructions for how to make it comes from the DNA (deoxyribonucleic acid)

BUT, there are many steps between a strand of DNA and a protein

Let’s review DNA first• DNA is double-stranded

• Adenine is always across from Thymine

• Cytosine is always across from Guanine

• bases are held across from each other by weak hydrogen bonds

A--T

C--G

Making Proteins•Making proteins involves another step as you saw on the first slide

•First, a molecule called RNA is produced

•This process is called TRANSCRIPTION

RNARibonucleic acid

single stranded

also made of nucleotides

The nucleotides of RNAThey are slightly different than DNA

They have a sugar and a phosphate group like DNA does

The difference

Three of the nitrogenous bases are the same: Adenine (A) Cytosine (C) Guanine (G)

The last one is different: Uracil (U)

Instructions for a ProteinThe instructions to make a certain protein are

coded by the sequence of nucleotides in a strand of DNA (a gene)

These instructions get transferred from the DNA strand to an RNA strand through transcription

So how does this happen?

There are a number of steps in the process of making a protein

The first involves two different parts: RNA polymerase the gene’s promoter

A promoter is a certain order of DNA

that acts as a “start” signal for transcription

RNA polymeraseRNA polymerase is an enzyme

It binds to the promoter of a gene

This enzyme helps unwind and separate the two strands of DNA

The templateOne strand of the DNA acts as a “template” for

making the RNA

This means that the nucleotides that will form the RNA pair up with this strand

RNA polymerase helps make this happen

Base Pairing Rules Just like with DNA, the nucleotides only pair

with certain other nucleotides

If there is a Thymine on the DNA strand, Adenine still pairs with it

If there is an Adenine on the DNA strand, it now pairs with Uracil

Cytosine pairs with Guanine just like before

Some covalent bonds are involved

As the RNA nucleotides get added to the strand of RNA that is forming, they are forming covalent bonds

The covalent bonds occur between the nucleotides of the RNA

How it endsTranscription keeps going until RNA polymerase

reaches a “stop” signal on the DNA

RNA polymerase falls off of the DNA and releases the RNA molecule

The DNA then winds back up

Animations:http://www.dnalc.org/resources/3d/12-transcript

ion-basic.html

http://www.youtube.com/watch?v=OtYz_3rkvPk

Textbook: http://bcs.whfreeman.com/thelifewire/content/chp12/1202001.html

Nebraska: http://croptechnology.unl.edu/animation/transcription.swf