Cell Structure and Function

• The cell is capable of surviving on its own or has the potential to do so.
• The cell carries out metabolism, responds to the environment, and can reproduce.

Cell Theory

Cell Types

• Prokaryote
• Eukaryote

Cell Components

• Membrane
• DNA
• Cytoplasm
• Ribosomes

Eukaryotic Organelles

• Nucleus
• Rough endoplasmic reticulum
• Smooth endoplasmic reticulum
• Golgi complex
• Lysosomes
• Vacuoles
• Mitochondria
• Chloroplasts
• Cytoskeleton

Cell Size

• Cells are limited in size by their surface-area-to-volume ratio.
• Eukaryotes can be larger due to the efficiency of their organelles.

Membrane Composition

• The membrane comprises a phospholipid bilayer.
• It has hydrophilic (polar) heads and hydrophobic (non-polar) fatty acid tails.

Fluid Mosaic Model

• The membrane is very fluid.
• Proteins are embedded throughout it.

Membrane Permeability

• The membrane acts as a selectively permeable barrier.
• Non-polar fatty acid tails restrict the movement of polar molecules across the membrane.
• Non-polar molecules can move across the membrane relatively easily.

Diffusion

• Particles move from areas of high concentration to areas of low concentration.
• The concentration gradient refers to the difference in particle concentration between two areas.

Mechanisms to Cross the Cell Membrane

• Diffusion allows non-polar substances with high concentrations outside the cell, and low concentrations inside, to pass through the membrane.
• Passive transport enables molecules with high concentrations outside and low concentrations inside to diffuse through the membrane with the aid of transport proteins.
• Active transport moves molecules against the concentration gradient, requiring energy in the form of ATP.
• The binding of ATP changes the shape of transport proteins, allowing particles to be carried against the gradient.
• Co-transporters carry more than one kind of molecule at a time.
• Endo- and exocytosis involve membrane-bound vesicles detaching from and binding to the cell's membrane, allowing material to be passed in and out.

Osmosis

• Osmosis refers to the movement of water across a selectively permeable membrane.
• Tonicity measures the relative concentration of solutes in a solution.
• Water moves from hypotonic to hypertonic solutions.

Energy

• Energy is the capacity to do work.

Thermodynamics

• The first law of thermodynamics states that energy can be converted from one form to another but not created or destroyed.
• In living systems, solar energy is converted into chemical energy via photosynthesis, and that chemical energy is used for cellular work (cellular respiration).
• The second law of thermodynamics states that the entropy of a system always increases without the input of energy.
• Entropy is a measure of randomness.
• Cells could not continue to exist in cohesive forms without the input of energy.

Chemical Reactions

• Anabolic reactions require the input of energy to build up larger molecules.
• Catabolic reactions release energy from breaking down larger molecules.

ATP/ADP Cycle

• ATP is the energy currency of the cell.
• ATP → ADP is a catabolic reaction, where released energy is used to do work.
• ADP → ATP is an anabolic reaction.

Enzymes

• Enzymes lower the activation energy of reactions.
• Enzymes catalyze and speed up specific chemical reactions.
• They function by binding specific substrates and facilitating chemical reactions, following the induced-fit model.
• Enzymes are sensitive to temperature, pH, salinity, etc.
• Metabolic pathways are coordinated chemical reactions (i.e., multiple steps leading to a product).
• These steps allow for a controlled release of energy.
• Redox reactions
• Electron transport chains

Explore the structural and functional components of cells, including prokaryotic and eukaryotic cell types, organelles, and the importance of the cell membrane. Key concepts such as cell theory, cell size limitations, membrane composition, and permeability will be covered. Learn about the fluid mosaic model and selective permeability.