Formed by autotrophs and disassembled by nearly all living things - carbohydrates are the primary source of chemical energy for the cell.
Formed by autotrophs and disassembled by nearly all living things - carbohydrates are the primary source of chemical energy for the cell. The elements carbon, hydrogen and oxygen are generally found in a 1:2:1 ratio in a carbohydrate (1:00). Carbohydrates primary function is to serve as a cellular fuel as monosaccharides (1:30) and disaccharides (2:46) whereas polysaccharides provide energy storage and structural support (3:38). It is important for organisms to have an appropriate amount of glucose available for cellular respiration (4:00).
The Question of the Day asks (6:19) When a glucose ring has the hydroxyl group on the same side as the CH2OH, it is in this form.
Thank you for listening to The APsolute RecAP: Biology Edition!
(AP is a registered trademark of the College Board and is not affiliated with The APsolute RecAP. Copyright 2020 - The APsolute RecAP, LLC. All rights reserved.)
Website:
EMAIL:
Follow Us:
Hi and welcome to the APsolute Recap: Biology Edition. Today’s episode will recap Carbohydrates
Zoom out:
Unit 1 - Chemistry of life
Topic 1.4-1.5
Big idea - Systems interaction
Ah Carbs - everybody’s favorite snack food and every dietitians enemy. The Atkins diet became infamous by encouraging everyone to consume bacon daily and vilified toast. Formed by autotrophs and disassembled by nearly all living things - carbohydrates are the primary source of chemical energy for the cell.
Let’s Zoom in:
There is a dead giveaway if the molecule you are looking at is a carbohydrate - its elements. Carbohydrates only contain the elements carbon, hydrogen and oxygen and in a very specific ratio. Think of a carbohydrate you are familiar with - probably glucose - C6H12O6. The elements Carbon, hydrogen and oxygen are generally found in a 1:2:1 ratio in a carbohydrate. These biological molecules can form linear chains of sugar monomers, some of which are branched, or ringed structures.
Carbohydrates primary function is to serve as a cellular fuel. Monosaccharides like glucose and fructose as well as disaccharides, such as lactose and sucrose are often used as energy sources for the cell. You may have noticed, but ending in -ose is a common pattern in naming carbohydrates. Glucose takes the main stage in AP Bio inside mitochondria and chloroplasts. As an aside, whatever you do, do not say that mitochondria are the powerhouse of the cell - this is AP Bio, we can do better. Most of the oxygen atoms found in these monosaccharides are in OH, hydroxyl, but one in particular is part of C=O, carbonyl. The position of the carbonyl within the monosaccharide further classifies the sugar. Be careful - a carbohydrate chain can look very similar to a fatty acid chemically. Furthermore, Glucose has an identical chemical formula to isomers fructose and galactose, but its atoms are arranged differently. Even these small differences are enough for enzymes to act upon the correct substrate.
We’ve just said that carbs have a 1:2:1 ratio of carbon:hydrogen:oxygen. So riddle me this: Sucrose is a disaccharide of the monomers glucose and fructose with the chemical formula C12H22O11- but why isn’t it C12, H24 O12, after all, I've doubled the amount of elements - right? Remember, that these two monomers join through dehydration synthesis (also known as a condensation reaction). Dehydrate - to take out water! A hydroxyl (OH) is removed from one monomer and a Hydrogen from the other. Now the exposed electrons can covalently bond at the remaining oxygen, forming a glycosidic bond. And so, if you take away two hydrogens and an oxygen from the doubled disaccharide, we are left with sucrose - C12H22O11. You might have even put some in your tea or coffee this morning - as sucrose is common table sugar.
Larger polysaccharides are used for structural support such as cellulose in plant cell walls or chitin in animal exoskeletons and fungi cell walls. Starch and glycogen and used for long term energy storage in plants and animals respectively. The primary contrast in polysaccharides is in their glycosidic linkages, branching patterns, and functions.
It is important for organisms to have an appropriate amount of glucose available for cellular respiration. In fact, the regulation of blood sugar levels is a great example of negative feedback. The polysaccharide glycogen is specifically stored in the liver and can be converted into glucose as needed. This conversion is controlled by insulin, a hormone produced by the pancreas. Imagine that you haven’t eaten in a few hours and your blood sugar levels are lower than normal. Under these conditions, your pancreas stops producing insulin, signaling the liver to break down glycogen into glucose through hydrolysis. Once blood glucose levels rise back to normal, the system shuts off. The opposite pathway is also possible. If blood glucose levels are too high, the pancreas produces insulin, which signals the liver to store glucose as glycogen - once again, returning blood sugar levels to the normal set points. Individuals with the disease diabetes must self monitor blood glucose levels due to low or ineffective insulin production.
OK - so what's the logic behind a low carb diet? The HArvard School of public health states - there is some research showing that a moderately low-carbohydrate diet can help the heart, as long as protein and fat selections come from healthy sources. The simple response is this: when carbs are in short supply, the body will seek out other sources of energy (namely lipids) - which can help get rid of some extra pounds.
Time for unit connections. You’ll find carbohydrates in Unit 2 when describing the role of the cell wall in maintaining cell structure and function, Connect to Unit 3 - cellular respiration and photosynthesis, and Unit 8 when discussing how the activities of autotrophs and heterotrophs enable the flow of energy within an ecosystem. Alright - what about the exam? You may be asked to correlate energy availability to carbohydrate structure, interpret enzyme activity with hydrolysis or even analyze a food web.
To recap……
Carbohydrates! Carbon, Hydrogen, and Oxygen arranged to provide immediate energy, energy storage, and structural support. These sugars are classified into monosaccharides, disaccharides, and polysaccharides. Blood glucose levels are regulated through negative feedback.
Coming up next on the Apsolute RecAP Biology Edition: Lipids
Today’s question of the day is about monomers.
Question of the day: When a glucose ring has the hydroxyl group on the same side as CH2OH, it is in this form.