Cell structure and function

• Cells are present in every single living organism
• Cells are the building blocks of life

Cell theory

• All organisms are made of cells
• Cells come from preexisting cells
• Cells are the smallest structures that can perform life functions

Cell membrane

• The Cell membrane is fatty
• It controls what comes in and out of the cell
• It adds structure to the cell
• It is a barrier that separates the cytoplasm from exterior substances
• It contains proteins

Cytoplasm

• Watery material that fills all space between organelles and the organelles with the cell

Cytosol

• The liquid part of cytoplasm is called cytosol
• Cytosol is 75%-90% water
• Cytosol has extra dissolved substances like salts and carbs
• It has other floating compounds like proteins
• Cytosol is where metabolic reactions occur

Organelles

• Structures within the cell that all have specific functions

Nucleus

• Almost all cells have a nucleus
• Some cells have more than one
• Some cells have zero, for example, mature red blood cells
• The nucleus has a double membrane to separate it from cytosol
• The nucleus contains DNA and the nucleolus, which help make ribosomes (proteins)

Ribosomes

• Joins aminoacids together to make proteins
• They are found free in the cytoplasm or attached to membranes

Endoplasmic reticulum

• Pairs of parallel membranes create channels from the cell membrane to the nuclear membrane
• They store, package, and transport proteins, carbohydrates, and lipids
• Rough ER: Ribosomes are attached to the membrane
• Smooth ER: No ribosomes, focused on carb and lipids

Golgi body

• Series of stacked, flattened membranes
• Usually near the nucleus
• Modifies proteins and packages them for secretion from the cell
• Performs final checks after ER (or Golgi Body) before excretion

Lysosomes

• Small spheres formed from the golgi body
• Contains digestive enzymes

Mitochondria

• Spread throughout cytoplasm
• Have a double membrane
• Cellular respiration occurs here
• Reactions generate energy for the rest of the cell to function

Cilia

• Short and numerous hair-like membrane that is outside the cell
• Beats back and forth to move the cell or other substances over it

Flagella

• Longer, and fewer membranes

Cytoskeleton

• Framework of protein fibres
• Provides shape and assists cell movements
• Microtubes: Hollow rods to keep organelles in place or move them
• Microfilaments: Move material around cytoplasm or move entire cell

Inclusions

• Chemical substances
• Is not a part of the cell
• Found in the cytoplasm

Centrioles

• Found in animal cells
• Involved in spindle formation during nuclear division

Fluid mosaic model

• Structure of a cell membrane

Phospholipid bilayer

• Made of phospholipid molecules that each have two parts: hydrophilic head that loves water, hydrophobic tail that hates water

Protein and cholesterol molecules in bilayer

• Cholesterol supports the bilayer structure
• Proteins extend from in to out of cell; carrier proteins, channel proteins, cell identity, receptor proteins

Membrane function

• Serves as a physical barrier
• Regulates what passes through
• Sensitive to changes
• Supports the cell by connecting to the cytoskeleton

Protein function

• Transports molecules through membrane quickly without using energy (passive)

Carrier proteins

• Binds to materials and transports across membrane (active/uses energy)
• Cell identity markers: Allows identification and analysis of specific types of cells
• Allows cells to identify and relate to the rest of the body

Cholesterol function

• Helps to stabilize the cell
• Regulates membrane fluidity during temperature changes
• Wedged in between phospholipid molecules

Membrane transport

• Semi-permeable/ differentially permeable (some move freely, others are restricted/controlled)
• Active transport requires energy
• Passive transport requires no energy

Simple diffusion

• Spreading of particles until evenly distributed
• Particles flow from an area of high concentration to area of low concentration
• Cell uses oxygen up, more o2 on outside of cell, 02 spreads through membrane to the area of low concentration
• Also works other way (co2)
• High concentration gradient = higher rate of diffusion.
• Water as a solvent

Osmosis

• Diffusion of water across membrane
• Substances such as sugar are solutes
• Water moves to areas with higher solute concentration
• Occurs even if the amount of water is the same on each side

Facilitated transport

• Proteins in cell allow substances to cross

Protein channels

• Pathways for hydrophilic molecules to move without touching hydrophobic tails
• Pathways are small, so ions and water move through easily
• Passive transport

Protein carriers

• Controls exit and entry of large molecules
• Specific to only certain molecules
• Can become saturated, and controlled by hormones
• Active process
• Grabs substances and deposits them

Vesicular transport

• Active process
• Movement across membrane in a vesicle
• Moves in both directions

Endocytosis

• Moving into cell
• Folds around substance and pinches around until contained
• Pinocytosis: Taking in of a liquid
• Phagocytosis: Taking in of solids

Exocytosis

• Exiting cell
• Same process
• Pushing out contents of vesicle into extra-cellular fluid

Simple diffusion

• Passive
• Transports water, oxygen, carbon dioxide, alcohol, fatty acids, steroids, ions such as sodium, potassium, calcium; lipids; soluble drugs

Osmosis

• Passive
• Transports water

Facilitated diffusion

• Passive
• Transports glucose, amino acids

Active transport

• Active
• Transports certain ions, glucose, and amino acids

Endocytosis

• Active
• Transports cholesterol, iron ions, micro-organisms, and cell debris, but only by certain specialized cells

Exocytosis

• Active
• Transports secretions, such as mucus or digestive juices