Cell Structures and Functions

• Cell organelles: maintain life processes and require input of materials and removal of wastes to support efficient and maintain life
• The cell membrane is the outer boundary of the cell that separates it from extra cellular fluid and other cells.

  Made of a phospholipid bilayer and proteins.

  Determines what comes into the cell and what leaves it.

  Semi-permeable: some substances in and out, and not others
• Cytoplasm is a jelly/watery material inside the cell, around the nucleus.

  Cytosol is the liquid portion of the cytoplasm.

  Mostly water 75-90%

  Rest is a mixture of dissolved substances and insoluble substances, such as proteins and fats.

  Location of metabolic reactions

  Helps to maintain osmotic pressure and flow of chemicals
• Nucleus is the largest organelle (oval shaped)

  Contains DNA. DNA contains info to determine the proteins the cell makes.

  Therefore, nucleus controls the structure and functioning of the cell.

  Inside is the nucleolus (Role in protein making)

  Nucleus has a double layered membrane (separates it from cytoplasm) with spaces called nuclear pores (allows movement of RNA in and out)
• Ribosomes are small sphere organelles.

  Found free in the cytoplasm or attached to membranes of other organelles (like endoplasmic reticulum)

  Location of protein synthesis - amino acids join together here to make proteins
• Endoplasmic Reticulum are pairs of parallel membranes that form a network of channels extending through the cytoplasm to nuclear membrane.

  Rough ER have ribosomes on the membrane, Smooth ER does not.

  Membrane of ER provides a surface for chemical reactions.

  Channels are for storing or transporting molecules.
• Golgi Apparatus is a series of flattened membranes stacked up on one another. Found usually near nucleus.

  modifies and packages proteins (brought from ribosomes, through ER to here)

  Vesicles are the small sacs of liquid on the membrane that break off the GA to carry proteins around or out of the cell. Vesicles can be formed from the cell membrane
• Lysosomes are small membrane bound spheres formed from the Golgi Apparatus.

  Contains digestive enzymes that break down large molecules.

  Joins with vesicles to breakdown material inside of the vesicle formed when entering the cell (Macromolecules and microorganisms) and also digest worn out organelles.
• Mitochondria is sausage shaped organelles found throughout the cytoplasm.

  Has a double membrane: Smooth outside. Folded inner membrane (cistae) provides large surface area.

  Is the site of cellular respiration reactions, making energy available for cells activities.
• Cilia and Flagella are fine projections that beat back and forth to move the cell or substances over the surface of the cell.

  DIFFERENCES:

  Cilia: short and numerous projections (e.g., lining trache or fallopian tubes)

  Flagella: longer and thinner, only one or two (e.g., sperm tail)
• Cytoskeleton is the framework of protein fibre:

  MICROTUBULES: hollow rods that keep organelles in place or move them around the cell.

  MICROFILAMENTS: moves material around the cytoplasm or moves the whole cell.
• All cells have three things in common:

  Cell membrane

  Cytoplasm

  Genetic Material
• Eukaryotic cells have organelles are found in plants and animals.

  Prokaryotic cells don’t have nucleus or membrane cells. But they do have genetic material (not inside a nucleus). Uni-cellular (e.g, bacteria)
• What's homeostasis?

  Internal balance; body systems working together to ensure that the cellular environment is kept constant.
• During cellular respiration...?

  glucose and oxygen are used to produce carbon dioxide, water and energy. Therefore clls need to be supplied with glucose and oxygen, while carbon dioxide and water are removed.
• Fluid Mosaic Model:

  The membrane is said to be fluid because of the molecules of which it is made are constantly changing position, and it is said to be mosaic because it is made of many different kinds of molecules.
• The main structure of the membrane is composed of phospholipid molecules, which are lipid molecules containing a phosphate group. The phospholipids are arranged in two layers, known as bilayer
• Each phospholipid molecule has a head that is hydrophilic (water loving) and a tail that it hydrophobic (water hating).
• There are cholesterol and protein molecules embedded in the bilayer. These molecules are important for the stability and integrity of the membrane.
• Cell membranes have a variety of protein molecules, including receptor proteins, channel proteins, carrier proteins, and cell-identity markers. Only 2% of of the cell membrane are protein, but they make up 55% of the mass of the membrane (since proteins are very large molecules)
• Functions of the cell membrane:

  • Acts as a physical barrier
  • Regulates the passage of materials
  • Sensitive to changes
  • Supports the cell