2 Cells

• Nucleus

  Large organelle surrounded by a nuclear envelope (double membrane) which contains many nuclear pores

  The nucleus contains chromosomes and a darker staining region known as a nucleolus.

  Nuclear pores allow substances to move between nucleus + cytoplasm

  Nucleolus synthesises ribosomes.
• Mitochondrion

  oval-shaped with a double membrane, the inner one is folded and forms structures called cristae - inside is the matrix

  site of aerobic respiration, which produces ATP

  Cristae increase the surface area

  Matrix contains enzymes involved in respiration

  
• Golgi apparatus

  These are a group of fluid-filled, membrane-bound, flattened sacs

  vesicles are often seen at the edges of these sacs

  They processes and packages new lipids and proteins

  Forms lysosomes

  
• Golgi vesicle


  small, fluid-filled, sac in the cytoplasm

  It's surrounded by a membrane and produced by the Golgi apparatus

  It stores lipids and proteins made by the Golgi apparatus and transports them out of the cell (via the cell membrane)

  
• Lysosome

  A type of Golgi vesicle

  A round organelle surrounded by a membrane, with no clear internal structure

  Contains digestive enzymes called lysozymes.

  These are kept separate from the cytoplasm by the surrounding membrane and digest invading cells

  
• Ribosome


  These lot are very small organelle made up of proteins and RNA; they aren't surrounded by a membrane

  They float free in the cytoplasm OR they're attached to the RER. Synthesises proteins - assembles them from amino acids.
• Rough endoplasmic reticulum (RER)

  A system of membranes enclosing a fluid-filled space in the cytoplasm. The surface is covered with ribosomes. Processes and transports proteins synthesised by ribosomes around the cell.
• Smooth endoplasmic reticulum (SER)

  Similar to RER, but with no ribosomes. Synthesises and processes lipids.
• Chloroplast

  A small, flattened structure surrounded by a double membrane. They also have membranes inside called thylakoid membranes - these membranes are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae - thin, flat, pieces of thylakoid membrane. The stroma is a thick fluid found in chloroplasts. Chloroplast is the site of photosynthesis - they contain chlorophyll which absorbs UV light. Some parts of photosynthesis happen in the GRANA, other parts occur in the STROMA.

  
• Cell wall

  A rigid structure that surrounds cells. Cell walls are made of cellulose in plants and algae but in fungi they're made of chitin. They support cells, resists stretching, and preventing osmotic lysis.
• Cell vacuole

  A membrane-bound organelle found in the cytoplasm. They contains cell sap - a weak solution of sugar and salts. The Surrounding membrane is known as the tonoplast. The cell sap keeps the cell turgid and supports the plant; it's also involved in the isolation of unwanted chemicals inside the cell.
• Eukaryotic cells

  • In complex multicellular organisms, eukaryotic cells become specialised for specific functions. Specialised cells are organised like this: TISSUES ➜ ORGANS ➜ SYSTEMS ➜ ORGANISMS
• Epithelial cells from the small intestines

  • Large SA provided by villi and microvilli. Large amounts of mitochondria which helps provide large amounts of energy (required to power active transport)
• Pancreatic tissue

  • Large amounts of RER for synthesis and transport of digestive enzymes (proteins). Large amounts of mitochondria because protein synthesis is energy demanding. Transport vesicles acting as a transport inactive enzymes to the cell surface.
• Red blood cells

  • Biconcave disk shape = large SA:V. Haemoglobin is small = never too far away from the membrane - short diffusion path. Small + flexible membrane = fit through narrowest capillaries, getting very close to respiring cells. Lack nucleus, mitochondria + ER = more space for oxygen.
• Sperm cells

  • Flagellum: propels the cell so that it swims towards the female gamete. Numerous mitochondria: provide energy for swimming. Head tipped with a special lysosome: digests through follicle cells.
• Prokaryotic cells

  Prokaryotic cells are much smaller than eukaryotic cells. They also differ from eukaryotic cells in the following ways: Cytoplasm that lacks membrane bound organelles. Smaller ribosomes = 70S. No nucleus; instead they have a single circular DNA molecule that is free in the cytoplasm + is not associated w/ proteins. A cell wall that contains murein, a glycoprotein. Many prokaryotic cells have: One or more plasmids (small, circular rings of DNA) - carries genes additional to those in the main genetic material, e.g. antibiotic resistance. A capsule surrounding the cell = stores toxic waste, stops it from drying out + prevents it from being attacked by WBCs. One or more flagella = for locomotion.
• Viruses

  Viruses are acellular and non-living, e.g. HIV. They only replicate when inside a living cell. Have a core of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid. Some viruses have an envelope of lipids + proteins that surround the capsid. Attachment proteins = glycoproteins projected from the capsid. The attachment proteins let the virus cling onto a suitable host cell.

  
• Magnification


  The number of times larger a sample appears to be under a microscope, compared to object's real size. Magnification = image size ÷ actual size of object. Put an 'x' before the magnification no.
• Resolution

  The ability to distinguish between 2 points on an image, the amount of detail.
• Optical microscopes

  • They're relatively inexpensive, They require minimal user training, They yield good results (in terms of identifying cell structures and activity). Max. magnification ×1,500. Max. resolution 0.2µm. Limited by the wavelength of visible light. Can observe living things. Does not use harsh chemicals. Cheap and easy to use. Non-coloured specimens must be stained for specific organelles. Low magnification / resolution.
• Transmission electron microscope (TEM)

  • Emits an electron beam through a very thin specimen. The beam is focused using a series of electromagnetic coil lenses (not glass as it would absorb e-). The electrons penetrate the denser parts of the sample LESS - this gives the contrast in the 2D image produced. Max magnification = ×500,000. Resolution = 0.0002µm. Very thin section of tissue preserved and stained with salts of heavy metals (e.g. uranium or lead) ➜ This causes e- to scatter differently - contrast. Placed in a vacuum - vital as air molecules scatter e-. Can see details inside cells. Sample must be in a vacuum - no water or air, so the sample is dead. Expensive and very hard to use. Harsh chemicals used in preparation which can cause artefacts.
• Scanning electron microscope (SEM)


  • Emits an electron beam directly onto a sample such that the electrons are reflected off it. The beam is focused using a series of electromagnetic coil lenses (not glass as it would absorb e-). Reflected e- are received on a scanner and used to produce a 3D image of surface features. Max magnification = ×500,000. Resolution = 0.0002µm. Very thin section of tissue preserved and stained with salts of heavy metals (e.g. uranium or lead) ➜ This causes e- to scatter differently - contrast. Placed in a vacuum - vital as air molecules scatter e-. Can see details of surface features. Sample must be in a vacuum - no water or air, so the sample is dead. Expensive and very hard to use. Harsh chemicals used in preparation which can cause artefacts.
• Cell fractionation

  Tissue to be studied cut into small pieces (minced) and placed into a COLD, ISOTONIC, BUFFERED solution. Homogenised using a homogeniser (sophisticated liquidiser), which releases the organelles from the cell. Filtrate is then placed in a test tube and centrifuged (spun) at low speed. Larger fragments (nuclei) collect at the bottom of the tube, forming sediment pellets and smaller ones remain near the top suspended in a liquid called the SUPERNATANT LIQUID. Pellets are then removed and the supernatant remaining is re-spun at a faster speed (more force). Continuing in this way smaller and smaller fragments will be recovered; the faster the speed, the lighter the organelles which make up the pellet become. The order at which the organelles separate are as follows: NUCLEI ➜ MITOCHONDRIA ➜ LYSOSOMES ➜ ER ➜ RIBOSOMES. In plant cells, CHLOROPLASTS come out after nuclei but before the mitochondria.

  
• Interphase

  The cell increases in size, makes new organelles, proteins and carries out its normal physiological functions (G1 phase). DNA is replicated by semi-conservative replication (S phase). The cell carries out its normal metabolic functions but also starts making spindle proteins, preparing for cell division. ATP production increased (G2 phase).

  
• Mitosis


  Mitosis allows growth, repair and asexual reproduction to occur. As mitosis begins, chromosomes are 2 strands joined in the middle by a centromere. The separate strands are called chromatids; 2 strands in the same chromosome = sister chromatids. There are 2 strands because each chromosome has already made an identical copy of itself during interphase. When mitosis is over, the chromatids end up as one-stranded chromosomes in the new daughter cell.
• Stages of mitosis

  Prophase: Chromosomes condense by supercoiling and folding. Nucleolus disappears. Centrioles migrate to opp. poles, forming a network of spindle fibres across it called the spindle apparatus. Nuclear envelope breaks down and chromosomes lie free in the cytoplasm. Metaphase: One or more spindle fibres attach to the centromere of each chromosome. Chromosomes line up in single file at the equator (A.K.A. the metaphase plate). Anaphase: Spindle fibres shorten causing the centromeres to divide. Sister chromatids migrate to opposite poles. Chromatids are known as chromosomes as they move independently to each other. Telophase: 2 sets of chromosomes form at each pole. New nuclear envelope forms around each set of chromosomes.
• Mitosis

  1. Chromosomes condense by supercoiling and folding

  2. Nucleolus disappears

  3. Centrioles migrate to opposite poles, forming spindle fibres

  4. Nuclear envelope breaks down

  5. Chromosomes line up at metaphase plate

  6. Spindle fibres shorten, sister chromatids migrate to opposite poles

  7. New nuclear envelope forms around each set of chromosomes

  8. Chromosomes de-condense, forming chromatin

  9. Nucleolus reforms

  10. Cytoplasm divides, forming two daughter cells
• After mitosis, the chromatids end up as one-stranded chromosomes in the new daughter cell
• Mitosis is a continuous process, but can be divided into a series of stages
• Prophase

  • Chromosomes condense and become visible
  • Nucleolus disappears
  • Centrioles migrate to opposite poles, forming spindle fibres
  • Nuclear envelope breaks down
• Metaphase


  • Spindle fibres attach to centromeres of chromosomes
  • Chromosomes line up at metaphase plate

  
• Anaphase


  • Spindle fibres shorten, causing sister chromatids to migrate to opposite poles
• Telophase

  • Two sets of chromosomes form at each pole
  • New nuclear envelope forms around each set
  • Chromosomes de-condense, forming chromatin
  • Nucleolus reforms

  
• Cytokinesis

  Cytoplasm divides, forming two daughter cells
• Mitosis and the cell cycle are controlled by genes
• If there's a mutation in a gene that controls cell division, uncontrolled cell division can occur, leading to the formation of tumours and cancers
• Cancer is defined as a tumour that invades surrounding tissue
• Cancer treatments

  • They are directed at controlling the rate of cell division in tumour cells by disrupting the cell cycle
  • They kill tumour cells, but also kill normal dividing cells
• Prokaryotic cell replication

  1. Replication of circular DNA and plasmids

  2. Division of cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and variable plasmid copies