Transcription and Translation

The Central Dogma of Molecular Biology: DNA --> RNA --> Protein Protein synthesis requires two steps: transcription and translation.

Before we get into transcription and translation, let’s review some vocabulary gene - coded DNA instructions that control the production of proteins in cells DNA - deoxyribonucleic acid, the genetic material that tells your cells how to make proteins What are the four nucleotide bases in the DNA code? RNA - ribonucleic acid. It carries out the instructions coded in DNA. What are the four nucleotide bases in RNA? mRNA - messenger RNA RNA polymerase - an enzyme that attaches to DNA at specific sequences to start transcription ribosomes - small particles made of protein that are found on the rough endoplasmic reticulum. They bind mRNA and tRNA during translation. codon - a three base sequence in DNA or RNA that codes for one amino acid

DNA Contains Codes Three bases in DNA code for one amino acid. The DNA code is copied to produce mRNA. The order of amino acids in the polypeptide (the protein) is determined by the sequence of 3-letter codes (codons) in mRNA.

Transcription To transcribe something is to copy it. In transcription, DNA is copied into mRNA. RNA molecules are produced by copying part of the DNA sequence into a complementary RNA sequence.

Transcription To transcribe DNA to mRNA, we need an enzyme called RNA polymerase. It is similar to DNA polymerase. During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of mRNA. Where does transcription take place?

How does RNA polymerase know what part of the DNA to bind to? How does it know when to start and stop? There are regions of DNA called promoters, which have specific sequences. Promoters act as signals in the DNA to tell RNA polymerase where to bind. There is also a similar sequence in the DNA that signals RNA polymerase to stop transcription.

RNA Editing Like a rough draft of a paper, many RNA molecules need to be edited before they are ready for translation. The DNA of many eukaryotes contains sequences called introns that do not code for any proteins and must be cut out of the RNA sequence. The remaining sequences that do code for proteins are called exons. To help you remember, think of it this way – INtrons go IN the trash

RNA Editing What is the point of this? Nobody knows for sure. RNA editing may play a role in evolution. Mutations in introns have no effect on protein synthesis, but mutations in exons will probably have an effect and change the protein that will be produced. Once the RNA has been edited, it is released to the cytoplasm and attaches to a ribosome on the rough endoplasmic reticulum so that translation can begin

Translation To translate something is to express it in another language. mRNA is translated into amino acids, which form chains called polypeptides, which get folded and shaped into proteins.

More Vocabulary! tRNA - transfer RNA, it transfers an amino acid to the growing polypeptide chain. Each tRNA molecule carries one particular amino acid codon - a sequence of three nucleotides that together form a unit of genetic code in a DNA or RNA molecule. Each codon codes for one amino acid amino acids - the subunits that make up polypeptides and proteins polypeptide - a chain of amino acids protein - a finished polypeptide that has been folded into shape

Translation Translation begins when an mRNA molecule in the cytoplasm attaches to the ribosome. As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought to the brought to the ribosome by tRNA. In the ribosome, the amino acid is transferred to the growing polypeptide chain

Video! During the video, write down at least one question you have about transcription and/or translation.

How do we find out what the fox says? In this activity, you will examine the DNA sequence of a fictitious fox. These foxes say different things that are determined by their genes. Our fake foxes have one gene that determines what phrases they say. Your job is to analyze the genes of its DNA and determine what the fox says. The gene sequences we will be using are much smaller than -real-gene sequences found in living organisms. Each gene has two versions that result in a different trait (the phrase that the fox says) being expressed in the fox.

How do we find out what the fox says? Each of the DNA samples on your worksheets was taken from volunteer foxes. The DNA was then transcribed to its complementary mRNA strand. Your job is to analyze the mRNA sample and determine what the fox says based on the sequence. You will choose one sample (the sequences from one fox) to analyze. No foxes were harmed in the making of this presentation.

You will also determine four other traits that the fox has The first gene determines what the fox says. The rest of the genes determine the fox’s fur color (brown or red), eye color (brown or black), tail length (short or long), and fur length (short or long).

The Codon Chart Use this codon chart to determine which amino acids are in your fox’s sequence.

Example The mRNA of gene 1 in the Ylvis Fox is GUC AGC AAA Looking at the codon chart, GUC = val, AGC = ser, and AAA = lys Looking at the table, the amino acid sequence (the polypeptide or protein) val-ser-lys results in the Ylvis Fox’s first phrase being “ring-ding-dingeringeding” Continue this process until you have decoded all five genes, and you will know what the fox says and what it looks like!

Example Once you have determined all five of your fox’s traits, draw a picture of your fox and give it a text bubble showing what it says

Just in case you were curious…