Transcription and Translation Building Proteins from DNA

Protein Synthesis When the cell (or larger organism) requires proteins, these are created in the cell – the process is called *What are some examples of proteins?

Creating proteins happens in two stages: 1.Transcription = *This occurs in the nucleus of eukaryotic cells 2.Translation = using the mRNA to create a *This happens at a ribosome in the cytoplasm OR at a ribosome attached to the rough endoplasmic reticulum

What is RNA? RNA: It’s the “working” molecule Found all over the cell: nucleus, mitochondria, chloroplasts, ribosomes, cytoplasm

Structure of RNA Single polynucleotide chain Contains the bases cytosine, guanine, adenine and uracil Contains a 5 carbon sugar called ribose *Is uracil a purine or pyrimidine? How do you know?

Compare DNA with RNA DNAFeatureRNA Sugar Bases Structure Length

Compare DNA with RNA DNAFeatureRNA DeoxyriboseSugarRibose Adenine, Guanine, Thymine, Cytosine BasesAdenine, Guanine, URACIL, Cytosine Double stranded, strands held together with hydrogen bonds StructureSingle stranded Long – several million nucleotides in length LengthMuch shorter – 100 – 1,000 nucleotides *Has 1 form: DNA Forms*Has 2 forms: Transfer RNA = tRNA Messenger RNA =mRNS

mRNA = Messenger RNA Messenger RNA = mRNA – copies the code from DNA during transcription and carries it out of the nucleus to the cytoplasm – Carries the plan for the polypeptide chain that folds into a protein – Remains a long and unfolded molecule

Transcription Transcription is the process of copying one side of the strand of DNA to mRNA 1.DNA is “unzipped” 2.RNA polymerase moves along one side of the DNA strand matching free nucleotides to the exposed bases 3.Forms a complimentary strand of mRNA

If the template strand of DNA has the following bases, what will the mRNA strand look like? A A T T G G C C A A C C T T A A A A T T A A C C G G T T G G A A T T T T

In order to build a polypeptide, mRNA must travel outside the nucleus (through a nuclear pore) to a ribosome

Translation Translation is the second process in protein synthesis: – uses the sequence of bases in mRNA to build a polypeptide chain that will fold into a protein – uses a ribosome as a platform for the construction of the polypeptide – uses a variety of 20 different amino acids strung together like beads on a necklace: these are the building blocks of the polypeptide chain – Uses tRNA to “interpret” the genetic code Amino acids Polypeptide Chain Protein

tRNA = Transfer RNA RNA folded up On one end a specific is attached On the other end 3 specific bases are exposed – called the different amino acids will have different bases exposed Amino Acid

If the anticodon changes, the amino acid that is attached will also change The same amino acids have the same anticodons C G U Ser G A A Amino Acid Gly

Process of Translation mRNA will attach to a ribosome Ribosomes match up the anticodons with the bases in mRNA Every three bases in the mRNA is called a codon that matches with the anticodons in the tRNA *Put a red box around the codons in the mRNA, label tRNA

Translation At the site of the ribosome, two tRNA units will attach to the mRNA their amino acids will be linked together with a peptide bond *Label the peptide bond *When the amino acids are linked together is this a condensation reaction or a hydrolysis reaction?

Once the bond has been made one tRNA will detach from the ribosome The ribosome moves down the mRNA strand ready to attach another tRNA unit When the new tRNA is in place, another peptide is formed between the amino acids This process continues to happen which builds a long polypeptide chain *What will the anticodons be for the next tRNA?

When the polypeptide chain is complete, the mRNA will have a “stop” codon This codon causes the ribosome, mRNA and polypeptide chain to release The polypeptide can then fold into a protein

Translation Animation: mat/molgenetics/translation.swf