The Connection Between Genes and Proteins


- Genes specify proteins
- DNA controls metabolism by directing cells to make specific enzymes and other proteins
- A gene determines the amino acid sequence of a polypeptide chain
- The two main processes in making a protein from a gene is transcription and translation

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- Transcription is the transfer of information from DNA to RNA (nucleotide to nucleotide)
- Translation is the transfer of information from nucleotide sequence in RNA to amino acid sequence in a polypeptide
- A nucleotide triplet is called a codon. They are used as a genetic code to specify amino acids
- When a start codon is recognized translation begins until it reaches a stop codon that signals it to terminate
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The Synthesis and Processing of RNA


- RNA synthesizes by using a strand of DNA after it is catalyzed by RNA polymerase
- RNA uses the same base pairing method except that instead of using thymine they use uracil
- At the start of a gene there are specific nucleotide sequences called promoters to signal the initiation of RNA synthesis
- In Eukaryotic cells RNA molecules are modified after transcription. Their ends are modified and RNA splicing occurs
- In RNA splicing introns are removed because they are non-coding regions unlike the exons that remain
- If exons are shuffled during this process it may contribute to protein diversity

The Synthesis of Protein


- Translation is directed by RNA to synthesize polypeptides
- tRNA transfers amino acids from the cytoplasm’s amino acid pool to a ribosome. The ribosome then adds each amino acid brought to it to the end of the polypeptide chain its creating
- tRNA molecules bear different amino acids at one end and anticodons on the other. The anticodon base-pairs with a commutationpointDNA.gifplementary codon on mRNA and the amino acid is what is added on to the polypeptide.
- There are three parts in translation: initiation, elongation, and termination
- Ribosomes perform all stages of translation and are made of protein and rRNA. They have binding sites for mRNA called P and A sites that hold tRNA’s as amino acids are linked in the growing polypeptide. The E site releases tRNA.
- Free ribosomes in the cytosol initiate the synthesis of all proteins but proteins that are made for membranes or export from the cell become attached to the endoplasmic reticulum
- In a prokaryotic cell translation of mRNA can begin while transcription is still taking place but in a eukaryotic cell the nuclear envelope separates the processes.
- Point mutations are changes in one base pair of DNA which can affect protein structure and function.
- Base pair substitutions, insertions, or deletions can occur and cause frameshift mutations that disrupt the mRNA reading