So far we have studied cells, their organelles and carbohydrates.
Sometimes we are so focused on individual topics that we forget to look at the ‘big picture’ or the application of this knowledge.
Scientists have used, what we know now of cells and carbohydrates, to make advancements in medicine, nutrition and agriculture.
As cell size increases the surface area to volume ratio decreases. This restricts the
maximum size of cells. Some organisms have adapted to overcome these restrictions.
We shall look at some of them now:
The nucleus is responsible for controlling metabolism in the cytosol. For efficient
control, it is important to maintain a critical nucleus to cytoplasm ratio. As cells
increase in size, this ratio diminishes. Suggest how some cells have adapted to this
challenge giving an example of such cells. [1mk]
Particular cells such as muscle cells in animals and haphae of fungi contain more than one nucleus. This allows for the movement via osmosis to occur efficiently since the volume ratio of the nucleus to cytoplasm would be in proportion. Also, in liver cells, due to cell volume and proliferative activity the cells swell which occurs due to osmotic stress.
Explain what is meant by cytoplasmic streaming. [2.5 mks]
Cytoplasmic streaming deals with the movement of nutrients, proteins and organelles within plant and animal cells. It involves a molecule of 2 proteins that moves 1 protein wrt the other. To move organelles, 1 protein must be fixed to a substrate and the motor protein moves organelles and molecules through the cytoplasm.
As the cell size increases the process won’t be as efficient since the movement of organelles and molecules would have to move further and it would therefore take longer.
Organelles and Human Disease
Organelles can contribute to a disease state in several ways. First, the organelle itself may be dysfunctional either because it contains one or more defective biomolecules that impair function, or because it has been damaged by exposure to harmful substances such as chemicals, heavy metals, or oxygen radicals. Second, an organelle can, through its normal function, exacerbate damage occurring elsewhere in the cell.
Pathophysiology is the study of the biologic and physical manifestations of disease as they correlate with the underlying abnormalities and physiologic disturbances. Pathophysiology does not deal directly with the treatment of disease. Rather, it explains the processes within the body that result in the signs andsymptoms of a disease.
For example the underlying pathophysiologic defect in type 1 diabetes is an autoimmune destruction of pancreatic beta cells. Following this destruction, the individual has an absolute insulin deficiency and no longer produces insulin. Autoimmune beta cell destruction is thought to be triggered by an environmental 2event, such as a viral infection. Genetically determined susceptibility factors increase the risk of such autoimmune phenomena. Since the pancreas no longer produces insulin, a type 1 diabetes patient is absolutely dependent on exogenously administered insulin for survival. People with type 1 diabetes are highly susceptible to diabetic ketoacidosis. Because the pancreas produces no insulin, glucose cannot enter cells and remains in the bloodstream. To meet cellular energy needs, fat is broken down through lipolysis, releasing glycerol and free fatty acids. Glycerol is converted to glucose for cellular use. Fatty acids are converted to ketones, resulting in increased ketone levels in body fluids and decreased hydrogen ion concentration (pH). Ketones are excreted in the urine, accompanied by large amounts of water. The accumulation of ketones in body fluids, decreased pH, electrolyte loss and dehydration from excessive urination, and alterations in the bicarbonate buffer system result in diabetic ketoacidosis (DKA). Untreated DKA can result in coma or death.
Describe the pathophysiology of the following diseases.
(i) Tay-Sachs disease [2.5mks]
(ii) Leigh’s disease [2.5mks]
(iii) Pompe’s disease [2.5 mks]
1) Tay Scah’s disease
- Rare inherited disorder
- Destroys nerve cells in the brain and spinal cord
- HEXA gene mutation
- HEXA gene allows the enzyme β-hexosaminidase A to be made
- The enzyme breaks down GM2 ganglioside
- Too much GM2 ganglioside causes the destruction of neurons
- Severe neurological disorder
- Mutation in 1 of over 30 genes in nuclear DNA
- These genes correspond with energy production via mitochondria
- In oxidative phosphorylation 5 protein complexes are involved which drives the production of ATP. The 5 complex are disrupted by the mutation
- Inherited disorder
- Build up of glycogen causes malfunctioning of organs, tissues and muscles
- GAA gene is mutated
- GAA gene is associated with the formation of the enzyme acidic α-glucosidase
- This enzyme functions simultaneously with lysosomes. It breaks glycogen to glucose
Honey, the first sweetener known to humankind, is the only sweetening agent that can be stored and used exactly as produced in nature. Bees process the nectar of flowers so that their final product is able to survive long-term storage at ambient temperature. Used as a ceremonial material and medicinal agent in earliest times, honey was not regarded as a food until the Greeks and Romans. Only in modern times have cane and beet sugar surpassed honey as the most frequently used sweetener. The bees’ processing of honey consists of (1) reducing the water content of the nectar (30% to 60%) to the self-preserving range of 15% to 19%, (2) converting the significant amount ofsucrose in nectar to glucose and fructose by enzyme actionand (3) producing small amounts of gluconic acid from glucose by the action of the enzyme. Most of the sugar in the final product is glucose and fructose, and the finalproduct is supersaturated with respect to these monosaccharides.
State the type of reaction occurring and the enzyme that the bees use to convert:
(i) sucrose to glucose and fructose [1mk]
(ii) glucose to gluconic acid (draw the structure of gluconic acid. [2mks]
The fructose in honey is mainly in the β-D-pyranose form. This is one of the sweetest carbohydrates known, about twice as sweet as glucose; the β-D-furanose form of fructose is much less sweet.
(iii) Draw β-D-Fructopyranose and β-D-Fructofuranose. [1mk]
The sweetness of honey gradually decreases at a high temperature. Also, highfructose corn syrup (a commercial product in which much of the glucose in corn
syrup is converted to fructose) is used for sweetening cold but not hot drinks.
(iv) Account for these observations? [1mk]
i) Bees use the enzyme invertase to convert surose to glucose and fructose via hydrolysis.
ii) The enzyme glucose oxidase converts glucose to gluconolactone, which is hydrolysed to gluconic acid.
iv) The cyclization of straight chain fructose results in pyranose or furanose. These are not as sweet as fructose ;when temperature increases the equilibrium shifts.
Although most textbooks show fructose exclusively in its furanose form, the predominant form of fructose (67% of total fructose) is β-D-fructopyranose, with the β- and α-fructofuranose forms accounting for 27% and 6% of the fructose, respectively.
Lactose exists in two anomeric forms, but no anomeric forms of sucrose have been reported. Why? [1mk]
Sucrose has 2 monosaccharides that contain glycosidic bonds where the anomeric carbons are associated. No mutarotation ours since there are no free anomeric carbons in the disaccharide.
Explain why pectin is sometimes added to fruit extracts to make jams and jellies. [1 mk]
Pectin holds cell walls together. It forms a barrier that aids in trapping liquids. It works well with aid and sugar to form a jelly like substance.
Insects use an open circulatory system to circulate hemolymph (insect blood). The ‘blood sugar” is not glucose but rather trehalose, an unusual, nonreducing disaccharide. Explain why trehalose is a nonreducing sugar. [2mks]
2 glucose molecules bonded by 1-1 α bond gives the nonreducing sugar trehalose. This bond allows trehalose to be resistant to acid hydrolysis. The enzyme trehalase is responsible for breaking these 2 glucose molecules for absorption into the gut.
The following words were matched with their descriptions. [3mks]
Chitin – Give rigidity and strength to exoskeletons.
Chondroitin sulphate – Contribute to the tensile strength of cartilage, tendons, ligaments, and the walls of the aorta.
Dermatan sulphate – Is a component of the extracellular matrix of skin also present in blood vessels and heart valves.
Hyaluronate – Is an important component of the vitreous humor in the eye and of synovial fluid, the lubricant fluid of joints in the body.
Lectin – Found in all organisms, are proteins that bind carbohydrates with high specificity and with moderate to high affinity
Peptidoglycan – Give rigidity and strength to cell envelopes.
Did You Know
‘In 1869, concerned over the precipitous decline (from hunting) of the elephant population in Africa, the billiard ball manufacturers Phelan and Collander offered a prize of $10,000 for production of a substitute for ivory. Brothers Isaiah and John Hyatt in Albany, New York, produced a substitute for ivory by mixing guncotton with camphor, then heating and squeezing it to produce celluloid. This product found immediate uses well beyond billiard balls. It was easy to shape, strong, and resilient, and it exhibited a high tensile strength. Celluloid was eventually used to make dolls, combs, musical instruments, fountain pens, piano keys, and a variety of other products. The Hyatt brotherseventually formed the Albany Dental Company to make false teeth from celluloid. Because camphor was used in their production, the company advertised that their teeth smelled “clean,” but as reported in the New York Times in 1875, the teeth also occasionally exploded!’