cell structure

• DNA

  Genetic material found in all living cells
• Cytoplasm

  composed mainly of water with dissolved substances such as ions, where the cell's important reactions take place
• Plasma membrane

  Surrounds the cell and encloses all the cell contents, has a bilayer consisting of lipids
• Resolution


  The ability to distinguish between objects that are close together
• Types of microscopes

  • Optical microscopes (sometimes known as light microscopes)
  • Electron microscopes
• Optical (light) microscopes

  • Use light to form an image, cannot be used to observe smaller organelles such as ribosomes, maximum useful magnification of about ×1500
• Electron microscopes

  • Use electrons to form an image, can be used to observe small organelles such as ribosomes or lysosomes, maximum useful magnification of about ×1,500,000
• Types of electron microscopes

  • Transmission electron microscopes (TEMs)
  • Scanning electron microscopes (SEMs)
• Transmission electron microscopes (TEMs)

  • Use electromagnets to focus a beam of electrons, gives high-resolution images, cannot be used to observe live specimens
• Scanning electron microscopes (SEMs)

  • Scan a beam of electrons across the specimen, the beam bounces off the surface of the specimen, give lower resolution images than TEMs
• Optical (light) microscopes

  • use of fluorescent stains to view cells
• Electron microscopes

  • freeze fracture to provide a planar view of the internal organisation of cell membranes
• Robert Hooke came up with the term "cells" in the 1660's after examining the structure of cork
• Main ideas of cell theory

  • All living organisms are made up of one or more cells
  • Cells are the basic functional unit in living organisms
  • New cells are produced from pre-existing cells
• Types of cells

  • Prokaryotic
  • Eukaryotic
• Prokaryotic cells

  • Have the simplest cell structure, lack a nucleus, include bacteria and archaea, range from 0.1µm to 5.0µm in size
• Structures common to most prokaryotes

  • 70S ribosomes
  • DNA in a loop
  • Cytoplasm
  • Plasma membrane
  • Cell wall
• Prokaryotic ribosomes

  Structurally smaller compared to eukaryotic ribosomes
• Prokaryotic DNA

  Generally in the form of a "naked" single circular DNA molecule located in the nucleoid, and smaller loops called plasmids
• Prokaryotic cytoplasm

  Site of many cellular reactions, contains 70S ribosomes, composed of a gel-like cytosol
• Prokaryotic cell membrane

  Composed of a lipid bilayer, controls substances entering and exiting the cell
• Prokaryotic cell wall

  Contains murein/peptidoglycan, acts as protection, maintains the shape of the cell and prevents the cell from bursting, can be used to classify bacteria as Gram positive or Gram negative
• Additional structures found in some prokaryotes

  • Plasmids
  • Capsules
  • Flagellum
  • Pili
• Prokaryotic capsule

  Also known as the slime capsule, helps to protect bacteria from drying out and from attack by cells of the immune system
• Prokaryotic flagellum

  Long, tail-like structures that rotate, enabling the prokaryote to move
• Eukaryotic cells

  • cytoplasm is divided up into organelles, this allows enzymes and substrates to be localised and optimal conditions to be maintained for certain processes
• Flagellum

  • Long, tail-like structures that rotate, enabling the prokaryote to move (a bit like a propeller)
  • Some prokaryotes have more than one
• vili

  • Shorter and thinner structures than flagella
  • Assist with movement, avoidance of attack by white blood cells,
• Shared key structures between animal and plant cells

  • Membrane-bound organelles, including a nucleus
  • Larger ribosomes (80S)
• Key differences between animal and plant cells

  • Plant cells have a cellulose cell wall, large permanent vacuoles and chloroplast
• Structural adaptations of specialised cells

  • Red blood cells are biconcave and do not contain a nucleus. This makes more space inside the cell so that it can transport as much oxygen as possible
• Nucleus

  • separated from the cytoplasm by a double membrane, which has many pores
  • Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus
• Endoplasmic reticulum


  • Surface covered in ribosomes (80S)
  • Formed from folds of membrane continuous. These flattened membrane sacs are called cisternae
  • Processes proteins made by the ribosomes
• Ribosomes


  • Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells
  • Each ribosome is a complex of rRNA and proteins.
  • 80S ribosomes are found in eukaryotic cells
  • Site of translation
• Mitochondria

  • The site of aerobic respiration within all eukaryotic cells
  • Surrounded by a double-membrane
  • contains enzymes needed for aerobic respiration, producing ATP
• Golgi apparatus


  • Flattened sacs of membrane called cisternae
  • Modifies proteins and lipids before packaging them into Golgi vesicles
  • The vesicles then transport the proteins and lipids to their required destination
• Chloroplasts

  • Surrounded by a double-membrane
  • Also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis
• Cell walls

  • Formed outside of the cell membrane and offer structural support to the cell
• Microtubules

  • Make up the cytoskeleton of the cell and are about 25 nm in diameter
  • The cytoskeleton is used to provide support and movement to the cell
• Microvilli

  • Cell membrane projections
  • Used to increase the surface area of the cell surface membrane in order to increase the rate of exchange of substances