Biological Molecules and cells

  • Created by: miaebony
  • Created on: 12-11-18 15:03

Eukaryotic Cells

  • Nucleus - Surrounded by the nuclear membrane, contains nearly all genetic information, and also contains the nucleolus.
  • Nucleolus - Creates RNA and ribosomes, which then travel to the cytoplasm (to be involved with protein synthesis).
  • Rough ER - Found near the nucleus, made up of Cisternae (flattened sacs), has ribosomes on outer surface and is responsible for folding/processing proteins.
  • Smooth ER - Same structure as the RER (without ribosomes) and synethesises/processes Lipids.
  • Golgi Apparatus - Membrane bound flattened sacs responsible for the modification of proteins.
  • Vesicles - Used to store/transport proteins.
  • Lysosomes - membrane bound spherical sacs containing digestive enzymes that are used to break down materials (eg, dead or invading cells).
  • Mitochondria - Round, double membrane organelles (with inner membrane Cristae) responsible for aerobic respiration, producing ATP.
  • Centrioles - In animal cells. They move chromesomes in cell division by forming spindle.
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Prokaryotic Cells

  • Pili - Allows bacteria to connect to each other, or other surfaces.
  • Plasmid - Small, circular double stranded DNA molecule. Often, genes provide bacteria with genetic advantages.
  • Mesosomes - Infoldings in the plasma membrane, that play a role in cellular respiration, which also increases surface area.
  • Capsule - Enhances the ability of bacteria to cause disease and can protect cells from engulfment by eukaryotic cells.
  • Nucleoid - Section where DNA is housed. It may also contain RNA, proteins and enzymes.
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Both Eukaryotic/Prokaryotic

  • Ribosomes - 70s in prokaryote and 80s in eukaryotic cells. made of 2 sub-units that translate genetic information from mRNA into proteins.
  • Cell wall - Supports cells. Made of cellulose in plant cells (eukaryotes) and peptidoglycan in prokaryotes.
  • Plasma membrane - Regulates the movement of substances into/out of a cell.
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The Cytoskeleton


A system of filaments of fibres that is present in the cytoplasm of eukaryotic cells (cells containing a nucleus)

  • Microfilaments: Contractile fibres formed from actin. Responsible for cell movement.
  • Microtubles: Made of Tubilin and form a scaffold (spiral) structure determining cell shape.
  • Intermediate Fibres: Give mechanical strength. 
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Magnification = Image size/Actual size. 

I = AM

Magnification is how much bigger the image is than the specimen.

Resolution is how detailed an image is. Specifically, how well a microscope distinguishes between two points that are close together.

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Types of Microscopes

  • Light Microscopes - Have a low resolution (max 0.2 micrometres μm). Usually used to look at tissues or whole cells as the max useful magnification is about x1500. These are the microscopes usually used in college.
  • Laser Scanning Confocal - Use beams to scan a specimen (usually tagged in a fluorescent dye). A computer generates a very clear image from the scan which can then be looked at.
  • Transmission Electron Microscope (TEM) - Uses electromagnets to focus a beam of electrons. Has to be vacuumed and only used on thin specimens. The max useful magnification is 500,000x and the resolution is 0.0002μm.
  • Scanning Electron Microscope (SEM) - Shows the surface of a specimen and can be 3D. It has a good magnification, but is less than the TEM at 100,000x, and also has a lower resolution at 0.002μm.
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Molecules overview

Carbohydrates are made from monosaccharides and they can provide a fast source of energy. They contain C,H,O elements.

Lipids are composed of fatty acids & glycerol and are good at insulating and providing long term energy.They also contain C,H,O elements.

Proteins are made from sequences of amino acids. Proteins can be used for muscle development, with the immune system but also make up enzymes. Contain C,H,O,N elements.

Nucleic Acid is made from nucleotides and is responsible for coding of traits. Contain C,H,O,N,P elements.

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There are both Alpha and Beta glucose molecules - which have different positions of the (-OH) group. These are isomers.

- Disaccharides are joined by a glycosidic bond... made by monosaccharides.

Glucose properties

  • Polar (charge uneven)
  • Soluble in water (due to H+ bonds)
  • Therefore glucose divided into Cytosol of cell.


Glucose + galactose > lactose, joined by a 1,4 beta glycosidic bond.

Glucose + glucose > maltose, joined by 1,4 alpha glycosidic bond.

Glucose + fructose > sucrose, joined by alpha 1,4 glycosidic bond. (non-reducing sugar)

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Structure of Amylose and Amylopectin. Amylose is alpha 1,4 glycosidic bonds and unbranched. Amylopectin is branched, 1-4 and 1-6 alpha glycosidic bonds, which plants store, and because it is highly branched it may wind up in a spiral.


Highly branched 1-4 alph glucose. It is the main storage component in animal cells as it is insoluble, branched and compact so very good for storage.Glycogen is mainly stored in the liver and the muscles and provides the body with a readily available source of energy if blood glucose levels decrease.


Beta glucose joined by 1,4 glycosidic links. Alternative beta molecules are rotated 180 degrees. This makes very long, straight unbranched chains. (-OH) groups are projected from both sides. These long chains can join by the OH groups and make microfibrils, which are part of why a cell wall is so strong.

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One glycerol molecule and 3 fatty acids joined together in a condensation reaction. (3H2O released). Ester bonds are frmed which can be broken down by hydrolysis. Tryglycerides act as an energy store in plants and animals.


Phosphate, glycerol and 2 fatty acids. the phosphate group is hydrophillic, and the hydrocarbon tails are hydrophobic. Majority of the molecule is insoluble in water. The molecule forms a phospholipid bilayer with the hydrophillic phosphate group on the outside, and the hydrophobic tails on the inside. The cell membrane is a phospholipid bilayer.


Made from 4 small carbon based rings and a OH group at one end. OH is hydrophillic and rest is hydrophobic. Ideal to sit between the hydrophobic tails of the phospholipid bilayer. Regulates fluidity and strength of membrane.

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Biochemistry of Lipids

Fatty acids are said to be saturated if there are no C=C double bonds in the hydrocarbon chain. These fatty acids form straight chains and have high melting points.

Fatty acids are said to be unsaturated if there are C=C double bonds in the hydrocarbon chains. These fatty acids form bent chains and have low melting points.

If the fatty acids have more than one C=C double bond, they are said to be polyunsaturated.

Testing for Lipids (Emulsion test)

  • Add sample to a clean test tube. Simply add ethanol and mix by inverting several times. 
  • Add water to the test tube.
  • The formation of a cloudy white emulsion/precipitate indicated the prescence of a lipid.
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Benedict's Test


For reducing sugars

  • Add 2cm of the sample solution to a test tube.
  • Add an equal volume of benedicts solution and swirl to mix.
  • Leave the test tube in a boiling water bath for about 5 minutes.
  • Observe the colour during that time and then the final colour.
  • Do a control using distilled water.

For non-reducing sugars

  • First test will come back negative (for reducing sugars).
  • Test solution should be boiled with dilute HCL for a few minutes to hydrolyse the glycosidic bonds.
  • The solution should then be neutralised by adding small amounts of solid sodium hydrogen carbonate until it stops fizzing.
  • Test should then be done as before (with reducing sugars).
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  • Water is polar which means is has slightly positive and slightly negative (uneven) charges.
  • It forms weak hydrogen bonds.
  • Water has a high specific heat capacity (due to prescence of H+ bonds) which means it can absorb a lot of heat without significantly increasing its temparature, meaning its a stable environment for life.
  • Water molecules have the ability to stick to one another (cohesion) which can create surface tension, and also to other substances (adhesion). 
  • It has a high latent heat of vaporisatio which is a good coolant - and explains why we sweat when we are too warm
  • It is less dense as a solid (ice) which means it remains a stable environment as ice floats on top of water and insulates the surface beneath it to ensure remain of aquatic life.
  • Water is also a good solvent (due to being polar) which means that things are able to be absorbed by it, eg. vital things in our body, such as minerals carried by our blood.
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Amino Acids > A Polypeptide.

Proteins are made up of:

  • An amino group
  • 'R' group (variable)
  • Carboxyl group

Peptide bonding

Joined by a condensation reaction, the carboxyl and amino group lose a water molecule between them (H from amino and OH from carboxyl). 

Biuret test for proteins

Detects presence of proteins, peptide bonds form violet coloured complexes with copper ions in alkaline solution. Biuret reagent is used (Copper sulphate and sodium hydroxide). Blue if negative, purple if positive.

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Protein structure


A sequence of amino acids, wth peptide bonds involeved.


Coiling or folding of an amino acid chain (eg. Alpha helix or beta pleated sheet).


The overall 3-dimension shape of a protein molecule... Can involve hydrogen, ionic, disulphide hydrophobic and hydrophillic reactions. An example is pepsin.


Protein made of more than one polypeptide chain. Involves all the bonds above and an example is haemoglobin insulin.

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Globular/Fibrous Proteins


Almost spherical with hydrophobic R groups turned inward and a hydrophillic group on the outside. Has a irregular sequence, and ued for metabolic functions. Water soluble and include Haemoglobin, Insulin and Enzymes.


Have regular, repetitive sequences of amino acids. Usually insoluble in water. Form fibres, not folded into complex 3d shapes and includes collagen, elastin and keratin. More stable than globular proteins and are used for support and structure.

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