CELL STRUCTURE (Topic 1)

• All living organisms are made of cells
• Human are made up of eukaryotic cells. All eukaryotic cells contain a nucleus and membrane bound organelles.
• Animal and plant cells both contain:

  1. nucleus
  2. rough endoplasmic reticulum (rer)
  3. smooth endoplasmic reticulum (ser)
  4. Golgi apparatus
  5. mitochondria
  6. centrioles
  7. ribosomes
  8. lysosomes
  9. cell surface membrane
  10. cillia
  11. microvilli
• The nucleus is surrounded by a double membrane called the envelope containing pores which enable molecules to enter and leave the nucleus, the nucleus also contains chromatin and a nucleolus which is the site of ribosome production.
• Rough endoplasmic reticulum which is a series of flattened sacs enclosed by a membrane with ribosomes on the surface. RER folds and processes proteins made on the ribosomes. the ribosome is the site of protein synthesis
• Smooth endoplasmic reticulum is a system of membrane-bound sacs. SER produces and processes lipids.
• Golgi apparatus is a series of fluid-filled, flattened & curved sacs with vesicles surrounding the edges. The Golgi apparatus processes and packages proteins and lipids. It also produces lysosomes.
• Mitochondria are usually oval-shaped, bound by a double membrane called the envelope. The inner membrane is folded to form projections called cristae with a matrix on the inside containing all the enzymes needed for respiration.
• Centrioles are hollow cylinders containing a ring of microtubules arranged at right angles to each other. Centrioles are involved in cell division. Please note: Centrioles only exist in some species of lower plants

  (e.g. algal cells except red algae, some fern cells, male gametes of charophytes, bryophytes, ginkgo, cycads, seedless vascular plants, and moss cells).
• • Ribosomes are composed of two subunits and are the site of protein production
• A lysosome is a vesicle containing digestive enzymes bound by a single membrane.
• • The cell surface membrane surrounds the cell and controls what enters and exits.
• The cell surface membrane surrounds the cell and controls what enters and exits.
• Some animal cells may contain cilia on their surface membrane. These are small hair-like structures composed of microtubules in a ‘9+2’ formation. This allows movement of cilia therefore allowing movement of substances along the surface of the cell
• Microvilli are finger-like projections of the cell membrane which increases the cell's surface area. They line organs like the small intestine to maximise nutrient absorption.
• The following are only in plant cells:

  1. Vacuole
  2. Cell wall
  3. Chloroplasts
  4. Plasmodesmata
• The vacuole is a fluid-filled sac present in plant cells, surrounded by a membranecalled the tonoplast. It contains mineral salts, sugars, amino acids, waste substances and pigments. Its role is to colour the cell to attract pollinating insects, act as a temporary food store and provide support through turgidity.
• • The cell wall (plant cells) is made of cellulose microfibrils. Its role is to strengthen the cell and prevent bursting due to osmosis.
• • The chloroplasts are small flat organelles. They are surrounded by a double membrane. It also contains thylakoid membranes which are stacked up to form grana and are linked together by lamellae. Chloroplasts are the site of photosynthesis.
• Plasmodesmata are small channels that pass through the cell walls of adjoining plant cells to allow communication between cells.
• Chromatin - DNA wrapped around proteins called histones. This forms chromosomes during cell division.
• Nuclear Envelope - A double membrane surrounding the nucleus. Pores on its outer layer allow molecules to enter or leave the nucleus.
• Nucleolus - A dense region within the nucleus where ribosomal RNA molecules are synthesised.
• Prokaryotic cells (such as bacteria) contain:

  1. Cell wall
  2. Capsule
  3. Plasmid
  4. Flagellum
  5. Pilli
  6. Ribosomes
  7. Mesosomes
• All cells come from preexisting cells through the process of cell division
• there are 2 types of cells, prokaryote (simple) and eukaryote (complex)

  "eu" means true, "pro" means before, "karyon" means nucleus; eukaryotes evolved from prokaryotes
• Cell wall is a rigid outer covering made of peptidoglycan
• Capsule is a protective slimy layer which helps the cell to retain moisture and adhere to surfaces
• plasmid is a circular piece of DNA
• flagellum is a tail like structure which rotates to move the cell
• Pili is a hair-like structures whichattach to other bacterial cells
• ribosomes are the site of protein production
• Mesosomes are the infoldings of the inner membrane which contain enzymes required for respiration
• Prokaryotic cells are unicellular and are typically 1–5μm in diameter. They do not contain membrane-bound organelles or a nucleus, and their ribosomes are (70S)
• Eukaryotic cells are larger than prokaryotes and have a true nucleus surrounded by nuclear envelope. The cytoplasm contains many different types of membranous organelle such as mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, vacuoles, etc.
• Viruses are non-living structures which consist of nucleic acid (either DNA or RNA) enclosed in a protective protein coat called the capsid, sometimes covered with a phospholipid layer called the envelope.
• prokaryotic cells have:

  1. circular DNA
  2. no nucleus so DNA is freely floating in the cytoplasm
  3. polysaccharide cell wall
  4. smaller ribosomes (70S)
• Plasma membrane lining

  Plasmodesmata are lined with the plasma membrane of the cells, creating a continuous cytoplasm between the cells
• Function of plasmodesmata


  Plasmodesmata play a crucial role in the transport of nutrients, signaling molecules, and other essential compounds between plant cells