MetabolismMetabolism is the collective term given to allphysical and chemical changes that take place intissues and cells. Catabolism refers to all processeswhereby larger molecules are broken down intosmaller ones and energy is released, such as thedigestion of food. Anabolism refers to all processeswhereby smaller molecules are built up into largerones, which requires the addition of energy. Thefunctions of metabolism can be summarised as theprovision of energy in the form of adenosinetriphosphate (ATP) and the exchange of carbonbetween molecules. Every process which usesenergy is dependent on the functions ofmetabolism, such as digestion, which breaks downmolecules into more usable substances for energyand raw materials. Glycolysis is the metabolicprocess of breaking down glucose to producepyruvic acid and ATP. Lipids are broken down intofatty acids and then, during glycolysis, are brokendown further to produce carbon dioxide, water andATP. Amino acids, produced during the synthesis ofproteins, can also be broken down to produceenergy.

The structure and functionof cellsThe cell is the basic building block of all life forms.There are many types of cell in the human bodywhich vary in size, structure and function – there isno such thing as a ‘typical cell’. However, cells doshare certain structural characteristics.

Structure of cells Cells are minute structures which can only bestudied using specialist viewing equipment calledmicroscopes. There are two types of microscope:light microscopes use light beams and are useful forviewing tissues and larger cells; electronmicroscopes use beams of electrons and providemuch greater magnification in order to study theinterior of human cells.

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Steroids have a similar structure to lipids;cholesterol is a typical example. Its functionsinclude formation of the plasma membranesand of the hormones oestrogen andtestosterone. Cholesterol is obtained fromanimal products but the body can make what itneeds in the liver. High levels of cholesterolcan lead to gall stones, blood clots, heartattack and stroke.

Fact file

Describe the structure and function ofcarbohydrates, proteins and lipids. (M)

Assessment task 1.1

Sources of energy1g of carbohydrate = 4.3 kcal1g of protein = 4.3 kcal1g of fat = 9.3 kcal

Fact file

Prefix cyt = cellscytology – the study of cells cytolosis – the destruction of cells cytoplasm – the protoplasm within cells

Fact file

Cells viewed under a light microscope (x300).

Before the first electron microscopes, in the1940s, the interior of human cells was described byscientists as a structureless soup. Since then, greatermagnification has highlighted the specific structureof cells and the complex reactions that take placewithin them. The structure of cells viewed throughelectron microscopes is sometimes called the ultra-structure, to emphasise the high levels ofmagnification required. Different parts of the ultra-structure are known collectively as organelles.

Unit 1: Scientific principles for beauty therapy 19

Cells viewed under an electron microscope (x1000).

Cell organelle Structure Function

Plasma/cell Outer or cell membrane: layer of Allows selective permeability, the passive membrane lipids sandwiched between two transport of fat soluble substances, and the

layers of larger protein molecules. active transport of charged particles.

Mitochondria Rod shaped with double membrane: outer Contains enzymes which convert ADP into membrane is similar to plasma membrane; ATP to provide energy. Mitochondria are inner membrane is folded into ridges. more abundant in high energy cells such as

muscle and liver cells.

Ribosomes Some attached to rough ER, some remain free Manufactures enzymes and proteins both for in cytoplasm; contain ribonucleic acid (RNA). export and for use within the cell.

Endoplastic Network of branches; similar structure to Contributes to cell support and channelsreticulum (ER) and continuous with plasma membrane. transport materials within the cell. Rough ER

Rough ER is studded with ribosomes. with ribosomes produces proteins and enzymes; smooth ER produces phospholipidsand steroids.

Gogli apparatus Similar to smooth ER with vesicles that Produces collagen and mucus and keeps all contain proteins and enzymes, lipids, secretions away from cytoplasm. Is best collagen and mucus. developed in secretory cells such as those in

the pancreas and salivary glands.

Lysosomes Powerful enzyme produced as vesicles Breaks down bacteria and destroys damaged from the Gogli apparatus. cell structures and extracellular matter,

e.g. osteoclasts in bone formation.

Nucleus Largest cell structure, containing a double Controls all cellular activities. Contains layered membrane continous with the ER. genetic material and nucleic acids (DNA Contains a tangled mass of chromatin made and RNA).up of DNA and protein.

Try to think of the names of some specific cellsof the human body and their functions.

Theory into practice

Structure and function of cell organelles:

Transport in cellsAs you have learnt, cells export some materials outof the cell body and also receive substances fromoutside. There are three methods of transport incells: diffusion, osmosis and active transport.

DiffusionDiffusion is the mixing together of molecules of aliquid or gas so that they become equally distributedbetween two regions. Molecules are in a constantstate of movement. In solids this is more of avibration in order that the substance remains fixed;however, in liquids and especially gases themolecules move freely within the structure orapparatus which contains them. In order for diffusionto take place there must be a difference in levels ofconcentration, known as the concentration gradient,and a permeable barrier (or no barrier at all).Molecules in an area of high concentration passthrough the barrier to an area of lower concentration,thus balancing the numbers of molecules on eachside and creating equilibrium. The state ofequilibrium stops further diffusion but the moleculesstill move around freely in their own region. The rateof diffusion is affected by body temperature and thesurface area of the barrier between the two areas ofdifferent levels of concentration: the higher thetemperature and the larger the surface area, thegreater the rate of diffusion.

The process of diffusion can be illustrated bygaseous exchange, which takes place duringrespiration: high levels of oxygen in the alveolidiffuse into the low levels of oxygen in the veins.Meanwhile, carbon dioxide diffuses from a region ofhigh concentration in the blood vessels to a regionof low concentration in the alveoli. (Respiration isdiscussed in detail in Unit 2: Human physiology,pages 57–9). The transport of gases in thebloodstream is a continuous process so the state ofequilibrium is not desirable. A high concentration ofoxygen in the lungs is constantly ‘topped up’ as weinhale more air, and carbon dioxide levels in theblood are replenished by the removal of wasteproducts from all areas of the body.

OsmosisOsmosis is a particular kind of diffusion thatinvolves the transport of a liquid from an area of lowconcentration to an area of higher concentrationthrough a semi-permeable membrane. A simpleillustration is the passage of water from a weak sugarsolution to a strong sugar solution through a

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Matrix

Folds in inner membrane

Outer membrane

Cisternae Ribosomes

Roughendoplasmicreticulum

Smoothendoplasmicreticulum

Free vesicle Attached vesicle

Identify and describe the basic structure andfunction of cells and cell organelles. (M)

Assessment task 1.2

Structure of mitochondria.

Structure of endoplasmic reticulum (ER).

Structure of Gogli apparatus.

Layers ofphospholipids

GlycoproteinPeripheral protein

Integral protein

Structure of plasma membrane.