1. + Protein Synthesis

2. + REVIEW: DNA plays 2 essential roles in organisms: #1: Allows cells to reproduce. How? DNA replication allows cells to pass along genetic information contained within an original cell. #2: Allows cells to maintain themselves. How? DNA allows for the synthesis of proteins (protein synthesis) which are necessary for cells to function and maintain themselves. We have already discussed DNA replication. Let’s take a closer look at why protein synthesis is important:

3. + Proteins: Complex molecules composed of one or more polypeptide chains made of amino acids and folded into specific 3D shapes that determine protein function. Gene: A sequence of nucleotides in DNA that performs a specific function such as coding for a particular protein. Phenotypical characteristics of organisms, such as the colour of a peacock’s feathers, are determined by proteins under the control of genes. Genes also direct the production of other physiologically essential proteins, such as antibodies, and hormones.

4. + If proteins are composed of polypeptide chains made of amino acids…what are polypeptide chains and amino acids? Polypeptide chain: A chain of amino acids linked together by peptide bonds. Amino acid: A monomer unit of a polypeptide chain that is composed of a carboxylic acid, an amino group, and a side group that differentiates it from other amino acids.

5. Amino acid Polypeptide chain Protein!

6. Hemoglobin: A protein Hemoglobin is a protein found in red blood cells.

7. Hemoglobin is composed of 2 polypeptide chains.

8. A “normal” polypeptide chain in hemoglobin: A “mutant” polypeptide chain in hemoglobin: If just one of these amino acids (glutamic acid) is substituted with another (valine) then a change in the shape of the whole red blood cell occurs. The change in amino acids changes the polypeptide chain which changes the shape of the hemoglobin protein. This causes the hemoglobin chains to stick to each other resulting in an overall sickle-shape of the blood cell.

9. In this case, a change in protein shape is cause for the disease sickle-cell anemia. We can see that making proteins (and ensuring sure they are made correctly) is a VERY important process after all!

10. So…how does DNA help make proteins? The Central Dogma of Molecular Genetics Page 237 in your Bio 12 text.

11. DNA holds the information to make proteins. DNA is located inside of the nucleus and cannot leave. Proteins are made outside the nucleus (in the cytoplasm of the cell) on ribosomes. Does anyone see the problem here? How do we get DNA’s blueprint for making proteins out to the ribosomes in the cytoplasm? (where proteins are built)

12. 1) DNA is too valuable to leave the nucleus (if it were damaged it could be catastrophic!) 2) When proteins are required, they are often required in large amounts. Since there are only 2 complete copies of DNA in the nucleus of a somatic (non-sex) cell, not many ribosomes could use a specific gene to make proteins at one time. 3) If DNA left the nucleus, it would have to re-enter the nucleus for storage, meaning it would need a re-entry strategy. Why doesn’t DNA just leave the nucleus to give information to the ribosomes?

13. So how do ribosomes make proteins when they do not have access to the DNA directly? The answer lies in mRNA (messenger RNA). DNA is transcribed into a complementary RNA message that encodes genetic information. Numerous copies of this message can be delivered to ribosomes in the cytoplasm. Ribosomes translate the message into polypeptide chains, which are processed into proteins. This entire sequence is described as the central dogma of molecular genetics.

14. The Central Dogma of Molecular Genetics Two main processes we will be concerned about within the central dogma: Transcription: the process in which DNA is used as a template for the production of complementary messenger RNA molecules. Translation: the process by which a ribosome assembles amino acids in a specific sequence to synthesize a specific polypeptide coded by messenger RNA.

15. What is the RNA stuff we keep hearing about? Just like DNA, RNA: -Is a nucleic acid -Is a polymer consisting of repeating units of nucleotides -Carries genetic information

16. 1)RNA contains a ribose rather than deoxyribose sugar. 2) Instead of thymine, RNA contains the base uracil. Uracil is able to pair with adenine in DNA. 3) RNA is single-stranded, while DNA is double-stranded 4) RNA can exist both inside and outside the nucleus, while DNA can only exist inside the nucleus How is RNA different from DNA?

17. The three main types of RNA: messenger RNA (mRNA): the end product of transcription of a gene, mRNA is translated by ribosomes into a protein. transfer RNA (tRNA): a form of RNA that is responsible for delivering amino acids to the ribosomes during the process of translation. ribosomal RNA (rRNA): a form of RNA that binds with ribosomal protein to form ribosomes.