In order to sustain life, our cells need four carbon-based organic molecules (carbohydrates, proteins, lipids, and nucleic acids), referred to as biological macromolecules. Choose two macromolecules from list above. For each macromolecule chosen, describe its chemical structure, give one example of specific molecule that is classified as this type of macromolecule, and explain its function in a living organism.
Carbohydrates are made up of the elements C, H and O as seen in the general formula (CH2O)n. One end of the carbohydrate contains a hydroxyl group (-OH) and the other a carbonyl group (C=O). An example of a polysaccharide, a long chain of carbohydrates, is cellulose. Cellulose is found in the cell walls of plant cells and gives plant cell a rigid structure. Lipids are another classification of macromolecules. Lipids consist mainly of hydrocarbons, chains of carbon atoms bonded to hydrogen atoms. Some lipids, like triglycerides, additionally contain a glycerol and three fatty acids. As hydrocarbons are non-polar, lipids tend to not dissolve in water, making them hydrophobic (i.e, waxes and oils). Lipids make up the cell or plasma membrane of all plant and animal cells.
Group 1 elements, the Akali Earth Metals, are the most reactive metals on the Periodic Table. Conversely, the Group 18 elements, the Noble Gases are inert (non-reactive). Explain this phenomena in terms of atomic structure.
An element’s relative reactivity is in part determined by the number of outer shell electrons, also called valence electrons, it contains. For example, during a chemical reaction in which an ionic compound is formed like table salt (Sodium chloride), sodium atoms will give away their outer shell electron to the chlorine atoms. Group 1 elements, like Sodium, all contain only one electron in their outer shell, making it very easy to give it up to another element during bonding with a different element. These elements are highly reactive since it takes very little energy to remove their outer shell electron. Nobel gases, on the other had, have a full outer shell of electrons. In most Noble gas elements, this means 8 outer shell or valence electrons. Helium is the exception and only has two outer shell electrons. Since the noble gases have a full outer shell, they neither give up or can take on extra electrons, thereby making them non-reactive.
The central dogma of biology explains that DNA is used as a template to make proteins in living organisms. Explain in detail how this process works in a eukaryotic cell.
In eukaryotic cells (i.e. skin, muscle, liver cells), DNA is used to make various types of proteins. This happens in a two part process called protein synthesis. The first part of protein synthesis takes place inside of the nucleus. During transcription, the first part of protein synthesis, a portion of the cell's DNA that codes for a specific gene is transcribed into mRNA (messenger RNA-a single stranded nucleic acid). As you will recall, DNA is a polymer made of adjoining nucleotides which contain a phosphate group, a five carbon sugar and one of the four nitrogenous bases (guanine, cytosine, adenine and thymine). During transcription, an enzyme called RNA Polymerase adds complimentary nucleotides to the template strand of the DNA in order to build the mRNA. It should be noted that mRNA does not contain thymine and is replaced with uracil. For example, a segment of the DNA might read: ATTCG and the corresponding mRNA strand would read: UAAGC. Once transcription has been completed, the mRNA can leave the nucleus through a nuclear pore and enter into the cell's cytoplasm. Translation is the second part of protein synthesis and takes place outside of the nucleus at a ribosome, a protein-making organelle. During translation, codons (a 3-lettered sequence of nucleotides) are translated into corresponding amino acids, the building blocks of proteins. This is a three-step process that includes the following stages: initiation, elongation, and termination. The initiation stage begins the process of translation, as signalled by the translation of the start codon, AUG. This process is done with the help of another type of RNA called tRNA or transfer RNA. The tRNA is a clover-shaped nucleic acid that contains an anti-codon, a 3-lettered sequence of nucleotides that bind to a complimentary sequence of codons on the mRNA. The tRNA moves through the cytoplasm to the ribosome, picking up a corresponding amino acid that it's anti-codon specifies for, and carries the amino acid to the mRNA. As the codon on the mRNA and the anti-codon on the tRNA bind, the amino acid on the tRNA is released. As each tRNA enters the ribosome it carries out this same function, thereby creating a long strand of amino acids, called a polypeptide. This is referred to as the elongation stage of translation. This process is repeated until the the stop codon has been reached on the mRNA. Once the stop codon is translated, the polypeptide is released. This is referred to as the termination stage. Once the polypeptide is released from the ribosome it undergoes some additional processing to turn in into a functional protein.