year 11 biology lesson 3: biological macromolecules

YEAR 11 BIOLOGY LESSON 3: BIOLOGICAL MACROMOLECULES

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1. Substances in Cells

Students:

Investigate cell requirements, including but not limited to:

- Suitable forms of energy, including light energy and chemical energy in complex

molecules.

- Matter, including gases, simple nutrients and ions.

Introduction to Biological Macromolecules

In the previous lesson, we learnt about how each cell is made up of many

organelles which each have their specialised functions. But what if we go one

step further – what are organelles made up of?

Everything in our body is composed of biological macromolecules.

– What does the term 'macromolecule' means?1

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– There are four classes of macromolecules found in cells that you must

learn about: carbohydrates, lipids, proteins and nucleic acids.

– Macromolecules can be considered as long polymers made up of

smaller repeating units called monomers. You will be able to see this

on the following page.



Below is a summary of the macromolecules we will be studying this lesson.



2. Carbohydrates

Carbohydrates are Composed of C, H and O

You may have heard about carbohydrates in the context of foods and diets.

– Some examples of carbohydrates are sugars and starch.

– Can you think of some foods that are rich in carbohydrates?2

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Carbohydrates are composed of carbon, hydrogen and oxygen atoms.

Carbohydrates can be categorised as monosaccharides, disaccharides and

polysaccharides.



Monosaccharides

Monosaccharides are the most basic units of carbohydrates.

– Some examples are glucose, fructose and galactose.

– They can all exist as a ring-like structure as depicted below.

By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

You may have heard of glucose from Junior Science.

– What is the name of the process that produces glucose from

sunlight? Write the word equation for this process.3

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– What is the name of the process that releases energy from glucose

in a usable form for cells? Write the word equation for this process.4

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These basic monosaccharides are important in the storage of energy, and

as building blocks for more complicated carbohydrates.


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Disaccharides

As the name suggests, disaccharides are made up of two monosaccharide

units joined together.

By CNX OpenStax [CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons

– For example, the reaction between a glucose and fructose monomer

produces the disaccharide sucrose.

– What is another common name for sucrose?5

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Here are some other examples of disaccharides.


– Where would you expect to find lactose?6

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– Maltose is found as a component of malt, in germinating seeds, and

as caramelised glucose.



Polysaccharides

Polysaccharides are made up of thousands of repeating monosaccharide

units, most commonly glucose. This is illustrated below.


Polysaccharides can play a structural role in cells.

– Cellulose is a sturdy material found in the cell walls of many plant

cells. In fact, it is the most abundant plant fibre on Earth!

– What is the role of the cell wall?7

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Polysaccharides can also be used for short-term energy storage. Two forms

of energy storage are shown below.


– In plants, energy is stored as starch. It can exist in two forms,

amylose and amylopectin.

– Why might starch be found in the chloroplasts of some plant cells?8

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– In animals, energy is stored in branching structures called glycogen.

They are found within mitochondria of liver and muscle cells.

– Why might glycogen be found in the mitochondria of some animal cells?

Hint: what is the role of mitochondria?9

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Testing for Starch Using Iodine

Iodine solution can be used to test for the presence of starch.

– Can you recall which class of macromolecules starch belongs in?10

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– Which substances or foods are rich in starch?11

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Iodine is normally a deep orange solution that turns dark purple in the

presence of starch.

Source: https://c1.staticflickr.com/5/4086/4966121581_9022b771bf_z.jpg

– Which of the test tubes above contains starch?12

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– Since this test is so simple, it is commonly used to test for the

presence of starch in plant experiment, as we will see in Lesson 5!



3. Lipids

Lipids are Composed of C, H and O

Lipids are more commonly known as fats and oils. They are composed of

long chains of carbon, hydrogen and oxygen atoms, like carbohydrates. An

example of a lipid is shown below.


Lipids have many important uses. They are essential for the body to function

properly, although too much of the wrong kinds of fats are unhealthy.

– Lipids make up the cell membrane in cells. We will learn more about

the cell membrane and its structural role in the next lesson.

– They are also important in long-term energy storage.

– Some steroid hormones are synthesised by cholesterol, a type of

lipid. Can you recall which organelle was primarily responsible for lipid

synthesis in the cell?13

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– Waxes are another type of lipid that is important in forming waterproof

coatings, for example, the inner surface of your ear canals!



4. Proteins

Proteins are Composed of C, H, O and N

Proteins are by far the most abundant and diverse group of macromolecules

found in the human body.

– Which organelles are required to synthesise proteins?14

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– Since proteins are so enormous and complex, there are many different

levels of protein organisation, summarised below.




Protein Structure

Proteins are long polymers of amino acids, made of carbon, hydrogen,

oxygen and nitrogen. The general structure of an amino acid is shown below.


– The 'R' group is actually a side chain that can be replaced by a series

of different atoms. This means that amino acids are variable and in

fact, there are 20 different amino acids that make up protein.




Amino acids can join together to form longer chains, as seen previously.

– As more amino acids join on, they form a long polypeptide chain. This

sequence of amino acids is called the primary structure of a protein.

– The chain can fold and form repeating structures, such as helices

and sheets. This constitutes the secondary structure of the protein.

– The polypeptide chain can keep folding to form a large three-

dimensional structure, known as the tertiary structure of a protein.

– Finally, two or more polypeptide chains can fold together to form the

functional protein. This is known as the quaternary structure.

Because there are so many different amino acids which can each join up to

form different sequences, there are millions of possible different proteins!

– Immunoglobulins, or antibodies, are proteins that are involved in

immunological defence. They bind to antigens on bacteria, viruses and

other foreign organisms.

– Enzymes are proteins that act as catalysts in the human body. They

speed up and facilitate chemical reactions.

– Haemoglobin is an example of a transport protein. It is found in red

blood cells and carries oxygen around to our tissues. In fact, the

diagram above is actually of haemoglobin.

– Keratin is an example of a structural protein which contributes to the

structure of hair, fur, claws and hooves.

– Some hormones, such as the human growth hormone and insulin, are

also proteins.

year 11 biology lesson 3: biological macromolecules

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