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All organisms exchange substances with their surroundings.

Single cell organisms that respire aerobically need to absorb oxygen and get rid of carbon dioxide. Also need to absorb nutrients and get rid of waste products.

This happens by simple diffusion.

Large multicellular organisms can not rely on simple diffusion - distances are too great and would take too long.

Key term - Diffusion - the movement of a substance from a high concentration to a low concentration.

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Eukaryotic

*Complex

*Include - animal cells, plant cells, yeast, fungi and algae

*Has a cell membrane, cytoplasm, DNA.

*Membrane bound organelles such as mitochondria.

*DNA is contained in the nucleus.

DNA is bound to proteins called histones. Together these form a complex called chromatin.

Prokaryotic

*Simpler and smaller

*Include - bacteria

*Has a cell membrane, cytoplasm, DNA.

*DNA floats freely in the cytoplasm or is found in small circular molecules called plasmids (not associated with proteins).

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Erythrocytes

Oxygen binds to the haemoglobin to carry this around the body.

No nucleus

Biconcave disc - increased surface area allows more efficient diffusion of oxygen in and out of the cell.

Elastic plasma membrane - allows the sell to change shape allowing the red blood cell to squeeze through narrow capillaries.

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Neurons

Conduct electrical impulses through the nervous system.

Electrical impulses follow one direction only.

In the PNS the neurons conduct towards the CNS

Motor neurons conduct impulses away from the CNS

Receptors - detect pressure / temperature for example and convert this into electrical impulses.

Effectors - muscles or glands that secrete hormones or enzymes.

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Relatively unspecialised

Flattened cells.

Supported by a basement membrane that make up the epithelium.

Well suited to exchange surfaces such as the lungs/gut/kidneys

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Male gametes

Highly specialised to enable them to deliver the haploid nucleus.

Contains genetic information.

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Female gamete

Much larger than sperm cells.

Released from ovarian follicle during ovulation.

Haploid nucleus containing genetic information

Gel layer protects the ovum when it is released.

Acrosome of the sperm binds to the gel layer.

After fertilisation the zygote divides several times without an overall increase in size.

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Make up skeletal muscles

Can be 300-3000 times longer than most cells.

Multiple nuclei

Often referred to as muscle fibres.

Striated refers to striped appearance under a microscope.

Function - contract in order to move bones and enable movement.

Their cell length allows them to contain the proteins involved in muscle contraction.

Formed by fusion of many individual cells during development which is why they have multiple nuclei.

Multiple nuclei mean that protein synthesis is more efficient.

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Used for growth and repair within the body e.g.

proteins in muscles, ligaments and tendons

enzymes involved in all cellular processes.

proteins in skin, nails and hair.

Applying knowledge -

The structure of an enzyme (a type of protein) determines how, or if even, it works.

Mutations in proteins can support us in understanding cancer development.

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Basic units of proteins are amino acids.

All amino acids have an amino group and a carboxyl group, but a different R group (sometimes called side chains).

Amino acids are joined together in a condensation reaction, forming a peptide bond.

Hydrolysis is the reverse, when water is used to split the bond.

Hydrolysis reactions are important in digestion.

Many amino acids are joined by peptide bonds a polypeptide is formed.

A protein is made up of one or more polypeptides. Folded into specific three dimensional shape.

Primary structure - sequence of amino acids in the chain. Does not allude to any recognisable structure.

Secondary structure - polypeptide chain folded into various sequences. ie alpha helix, beta sheet.

Tertiary structure - describes its three dimensional shape held together by various bonds and forces.

Quaternary structure - Many functional proteins are formed by two or more polypeptide chains. Eg, haemoglobin - consists of 4 polypeptide chains

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Basic units of carbohydrates - monosaccharides

Monosaccharides are composed of carbon, hydrogen and oxygen.

examples of monosaccharide - fructose, glucose.

Monosaccharides , when combined in pairs - disaccharides.

Formation of a disaccharide through condensation reaction.

The bond between the monosaccharides is called a glycosidic bond.

Polysaccharide - a polymer of many monosaccharide units joined by glycosidic bonds.

Used in the body - as a source of energy. Glucose stored in the liver and muscle cells as glycogen (a polysaccharide containing thousands of glucose units joined by glycosidic bonds).

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Lipids are not polymers

(A polymer is a large molecule made up of repeating smaller units called monomers).

They are formed in condensation reactions.

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Understand the purpose of each stage of the cell cycle

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Understand the purpose of each stage of the cell cycle

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The cell cycle consists of interphase and mitosis.

Mitosis

stages of mitosis listed below.

(During interphase the chromosomes are too long and thin to be seen with a light microscope)

Prophase - chromosomes become visible. Nuclear envelope disappears. The chromosomes can be seen to consists of two chromatids joined together. (Chromatid - one of a pair of identical chromosomes)

Metophase - Chromosomes arrange themselves at the mid-line of the cell (equator).

Anaphase - Chromatids of each pair migrate to opposite poles of the cells. By the end of anaphase the term chromatid is no longer used, they can be called chromosomes.

Telophase - Two sets of chromosomes collect at opposite poles of the cell. Nuclear envelope reforms around each set of chromosomes. Telophase is the end of mitosis.

Cytokynesis - cytoplasm divides to form two daughter cells.

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Enzymes are biological catalysts - speed up reactions in cells.

The structure of the enzyme determines the function -

The binding of the substates to the active site will depend on

the shape of the active site (the tertiary structure)

bond formation between the substrates and amino acid R groups at the active site. Could be hydrogen bonds or ionic bonds.

The shape of the active site is complementary to the shape of the substrate(s).

Specific for that substrate. (like a key and lock or jigsaw piece).

If there is a change in the shape of the protein and therefore the active site, the substrate will no longer bind effectively.

Key terms

substrates - substances on which the enzyme acts.

active site - the part of the enzyme where the substrate binds

denatured - the bond in the (enzyme) protein becomes weak so loses it's structure, therefore the shape changes along with the shape of the active site and the substrate no longer fits correctly making the enzyme less effective/ineffective.

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For efficient exchange the surface area must be large in comparison to the volume. (Think of all our learning around the lungs, digestive system and kidneys for example, they are designed with a large surface area and walls of the structures are only a single cell thick).

When the surface area is small compared to the volume organisms can not rely on simple diffusion across the whole body system. Specialist exchange and transport mechanisms are required to maximise the the rate of diffusion (eg lungs, gills, heart, circulatory system).

More active animals - higher metabolic rate therefore need more substances such as glucose for aerobic respiration.

This increases the need for specialised exchange and transport mechanisms.

A mouse for example has a larger surface area to volume ratio means an increased heat loss. Therefore they need to generate more heat from respiration , which in turn increases their need for more glucose and oxygen within the cells, and also explains their higher heart rate.

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Cell surface membrane and cellular exchange

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Cell surface membrane and cellular exchange

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Phospholipid bilayer - stable structure consisting of hydrophilic head group and hydrophobic tail. See diagram below.

Either side of the membrane is an aqueous medium (meaning the solvent is water).

The phospholipid bilayer acts as a barrier to diffusion of many substances.

Because the middle layer is hydrophobic - small non-polar molecules can pass through by diffusion.

Polar substances - water, glucose, amino acids or inorganic ions (eg. Na+, K+, Cl-) can not diffuse through the hydrophobic core of the bilayer.

- Partially permeable.

This means they need specialised transport mechanisms involving proteins and glycoproteins (proteins with glucose molecules attached) which are embedded into the phospholipid bilayer.

Example - small intestine.

Adapted to increase the efficiency of exchange.

Intestine is effectively a tube, the central space is called the lumen. Digestion occurs in the lumen.

The epithelial cells that line the lumen are specialised cells. The plasma membrane facing the lumen is folded into many tiny finger-like projections called microvilli. The microvilli greatly increase the surface area for absorption of the products of digestion.

Glossary - non-polar molecule is one where positive and negative charges are balanced, unlike polar molecules which have distinct positive and negative ends.

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Fluid Mosaic Model of eukaryotic plasma membrane

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Fluid Mosaic Model of eukaryotic plasma membrane

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Simple diffusion, facilitated diffusion and osmosis are all passive processes.

Do not require energy

Movement is always from high concentration to low concentration sometimes called a diffusion gradient.

Simple diffusion - small, non-polar molecules can move into the phospholipid bilayer and move across the membrane although the hydrophobic core can be a barrier to polar substances. (Substances that can move across,, non-polar include - carbon dioxide, oxygen, steroid hormones, lipids, fat soluble vitamins).

Facilitated Diffusion - Polar molecules (water, glucose, Na+, Cl-) can not diffuse across the membrane so they rely on facilitated diffusion.

Diffusion is assisted by proteins in the membrane.

Channel proteins act like pores in the membrane. Some of these can open and closed these are called gated channels. Ions and small polar molecules pass through these channels (including water).

Larger polar molecules (including glucose and amino acids) use carrier proteins. They are specific to the substance being transported which binds to the carrier protein. The carrier protein then changes shape which transfers the substance to the other side of the membrane.

The rules of diffusion still apply to both channel proteins and carrier proteins - substances move only from a high to low concentration.

Osmosis - particular type of facilitated diffusion where water moves across a partially permeable membrane from a high concentration of water molecules to a low concentration of water molecules. (Do not confuse this with a concentrated solution which has a high concentration of glucose for example and a low concentration of water molecules, where the substances are moving from high to low concentration).

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Facilitated diffusion through a channel protein 

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Facilitated diffusion through a channel protein 

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Facilitated diffusion by a carrier protein

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Facilitated diffusion by a carrier protein

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Active transport is a process that uses energy to move substances against a concentration gradient, from low to high concentration.

Involves carrier proteins that use ATP as the source of energy.

Often called protein pumps.

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Co-transport is the coupled movement of substances across a membrane.

One substance moves down the concentration gradient and this drives the movement of the other substance in the same direction.

Absorption of glucose from the gut is an example of co-transport.

Epithelial cells lining the small intestine have carrier proteins that only transport a glucose molecule together with a sodium ion.

A sodium ion pump in the plasma membrane pumps the sodium out of the epithelial cells into the blood capillaries. This lowers the concentration of sodium ions inside the epithelial cells.

The sodium ions move from the small intestine into the epithelial cells by diffusion via a co-transport protein which brings with them glucose molecules.

Once inside the epithelial cell, the glucose diffuses down a concentration gradient into the blood. As glucose is a polar molecule, this also requires a carrier protein. (see above diagram).

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Please note that R groups may be seen in different contexts, in different molecular diagrams.

It is an easy way to simplify the structure of large molecules, rather than writing the full structure. Not all R groups are the same.

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Fatty acid molecules repel water (hydrophobic).

Glycerol molecules attract water (hydrophilic).

Because a phospholipid is made up of a hydrophilic head and a hydrophobic tail.

These molecules can come together and form the fluid mosaic model which is important for all membrane functions.

Key term - Fluid Mosaic Model - describe the structure of the plasma membrane and how the parts are arranged. Proteins, lipids and carbohydrates that are found in the plasma membrane vary in shape, size and position which creates the mosaic pattern.

The relatively weak forces between the phospholipids means that the membrane can be considered fluid as the components can move through the membrane.

As well as their role in cell membranes lipids are also used within the body for

physical protection - fat deposits around organs to provide protection against physical shock

thermal insulation - subcutaneous fat lies below the skin surface to help retain body heat.

energy source

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Effect of temperature on rate of an enzyme-catalysed reaction

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Effect of temperature on rate of an enzyme-catalysed reaction

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The rate of a chemical reaction increases as temperature increases up to about 40 degrees.

This is known as optimum temperature as the rate of reaction is the highest.

Above 40 degrees the rate of reaction decreases rapidly.

This is because, as the temperature increases, the bonds that hold the tertiary structure of the protein weaken.

Increased temperature causes the atoms to vibrate more).

As a result the shape of the protein changes and therefore the active site shape has changed, therefore the substrate no longer fits correctly - the enzyme is therefore less/not effective.

Eventually the bonds become so weak that the protein loses it structure completely - denatured

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Enzymes - essential part in

all cell metabolic reactions

digestion (always involves hydrolysis reactions)

Proteases

eg trypsin - convert proteins into smaller polypeptides.

Some proteases convert polypeptides into dipeptides and/or amino acids.

Carbohydrases

eg amylase - convert long-chain polysaccharides such as starch into disaccharides.

amylase converts starch into maltose.

Other carbohydrases convert disaccharides eg maltose into monosaccharides such as glucose.

Lipases

convert triglycerides into glycerol and fatty acids.

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Fluid Mosaic Model of eukaryotic plasma membrane

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Fluid Mosaic Model of eukaryotic plasma membrane