UNIT 2 CELL STRUCTURE AND FUNCTION
Introduction to Cells
Overview
Cells are fundamental units of life.
Mastery of cell structures and functions is essential for understanding biology.
Video structure outlined:
Introduction to cells
Why cells are small
Internal organization of cells (compartmentalization and organelles)
Cell parts and functions
Membrane structure and function
Osmosis
Additional resources for study (checklist at apbiosuccess.com/checklist)
Basic Structure and Parts of Cells
Definition of Cells
Cells are the basic unit of structure and function in every organism.
Surrounded by a membrane that divides cytoplasm from the external environment.
Contain genetic information in the form of DNA.
Systems exist to maintain and replicate cells and genetic information.
Gene Expression
DNA is transcribed into messenger RNA (mRNA).
mRNA is translated into proteins by ribosomes.
Proteins serve various functions, including serving as enzymes that control metabolism.
Prokaryotic vs. Eukaryotic Cells
Prokaryotic Cells
Characteristics:
Smaller and simpler.
No nucleus; circular chromosome.
Additional chromosomal pieces known as plasmids.
Domains:
Represented in Archaea and Bacteria.
Eukaryotic Cells
Characteristics:
Larger and more complex.
Defined nucleus; multiple linear chromosomes with associated proteins.
Presence of mitochondria and various membrane-bound organelles.
Cell Size and Surface Area to Volume Ratio
Importance of Cell Size
Smaller cells have a higher surface area to volume ratio than larger cells.
Calculation Example:
For a cell of 1 micron:
Surface Area = 6 $ imes$ 1 $ imes$ 1 = 6
Volume = 1 $ imes$ 1 $ imes$ 1 = 1
Ratio = 6:1
For a 10-micron cell:
Surface Area = 600
Volume = 1,000
Ratio = 0.6:1
Consequence of Size
Larger cells cannot efficiently diffuse nutrients or waste due to decreased surface area to volume ratios.
Increasing Surface Area in Organisms
Purpose of Increased Surface Area
Enhances diffusion capacity of molecules and heat.
Mechanisms:
Thin sheets of tissue (gills in fish).
Large, flat surfaces (ears of elephants).
Highly folded surfaces (mitochondrial membranes and villi in intestines).
Example of Size Evolution: Whales
Whales' Size Evolution
Warm-blooded mammals lose heat in cold ocean water.
Larger size reduces surface area to volume ratio, conserving heat and energy.
Natural selection favored larger body sizes for energy savings and enhanced fitness.
Absence of Small Marine Mammals
Small mammals (mouse-sized) struggle with thermal regulation.
High surface area to volume ratio leads to significant heat loss.
Adaptations of larger marine mammals (like sea otters) include dense fur for insulation.
Metabolism and Body Size
Definition of Metabolism
Sum total of chemical processes in an organism.
Metabolic Rate vs. Basal Metabolic Rate
Metabolic Rate: Energy expenditure over time.
Basal Metabolic Rate: Energy use at rest under comfortable conditions.
Measurement of Metabolic Rate
Through oxygen consumption, carbon dioxide production, or heat production.
Endotherms vs. Ectotherms
Endotherms: Generate body heat from metabolism.
Ectotherms: Body temperature conforms to ambient temperature.
Endotherms require more food but can maintain activity across various temperatures.
Body Size and Energy Requirements
Larger endotherms need to consume more food (e.g., an African elephant vs. a mouse).
Relative metabolic rate decreases as size increases.
Example Comparisons:
Species
Daily Calories
Mass (g)
Calories/g per day
African Elephant
70,000
6,000,000
0.011
Human
2,250
62,000
0.036
Mouse
161
20
8.05
Etruscan Shrew
144
1.8
80
Metabolic Scaling Facts
High heart rate and respiration = high energy needs in smaller mammals.
Larger mammals can sustain themselves with lower metabolic rates and longer food intake intervals.
Cellular Compartmentalization and Endomembrane System
Cell Compartmentalization
Definition: Internal division of a cell's space into sections (e.g. lysosomes).
Advantages: Allows distinct internal chemistries; increases surface area for processes.
Comparison:
Prokaryotic Cells: Fewer compartments, simpler structures; e.g. thylakoids in cyanobacteria.
Eukaryotic Cells: Highly compartmentalized with various organelles (e.g. lysosomes, mitochondria).
Endomembrane System
Definition: Dynamic system of interconnected membranes (includes nuclear membrane, ER, Golgi, and lysosomes).
Functionality: Constant membrane and material flow between compartments.
Origin of Eukaryotic Cells
All eukaryotes arose ~1.8 billion years ago from prokaryotes via endosymbiosis.
Evidence for Endosymbiosis:
Mitochondria and chloroplasts have circular DNA, replicate independently, resemble bacterial structures.
Description of Eukaryotic Cell Parts and Functions
Nucleus: Stores/protects genetic information in DNA; contains nucleolus for ribosome assembly; has nuclear pores for molecule passage.
Ribosomes: Composed of rRNA/proteins; sites of protein synthesis; can be free-floating or bound to the rough ER.
Mitochondria: Convert food energy into ATP; contain DNA, ribosomes; have an inner membrane with folds (increasing surface area).
Endoplasmic Reticulum (ER): Interconnected channels (Rough ER has ribosomes; Smooth ER synthesizes lipids and detoxifies).
Golgi Complex: Membrane-bound sacs modify, package proteins for export or delivery within the cell.
Lysosomes: Contain hydrolytic enzymes for digestion; recycle cellular components and execute apoptosis.
Cytoskeleton: A network of protein fibers providing shape and enabling cell movement.
Centrosomes/Centrioles: Assist with cell division by creating spindle fibers.
Plant Cell Structures
Central Vacuole: Large, stores water, molecules, waste products, essential for turgor pressure.
Chloroplasts: Endosymbiotic origins; involve in photosynthesis-producing carbohydrates.
Cell Wall: Composed of cellulose; prevents over-expansion due to osmotic pressure, provides structural support.
Membrane Structure and Function
Cell Membrane: Selectively permeable; separates cell contents from the environment.
Phospholipid Structure: Consists of hydrophilic heads and hydrophobic tails forming a bilayer stabilized by Van der Waals bonds.
Fluid Mosaic Model: Describes membrane structure; components move laterally, resembling a mosaic.
Protein Integration:
Transmembrane Proteins: Span the membrane; have hydrophobic core.
Integral Proteins: Span membrane with one side in the cytoplasm.
Peripheral Proteins: Attach to the membrane surface.
Transport Mechanisms Across Membranes
Diffusion: Movement of molecules from high to low concentration; passive transport requiring no energy.
Active Transport: Movement against concentration gradient requiring energy (ATP).
Bulk Transport: Includes endocytosis (ingestion) and exocytosis (expulsion).
Membrane Potential and Ion Transport
Definition: Electrical charge difference across a membrane, created through ion pump expenditure of energy.
Mechanism: E.g., proton pumps in mitochondria contributing to ATP synthesis and neuron activity.
Tonicity and Osmoregulation
Osmosis: Diffusion of water from low to high solute concentration.
Terms:
Hypotonic: More water, less solute.
Hypertonic: Less water, more solute.
Isotonic: Equal concentrations.
Effects on Cells:
Shrinkage in hypertonic environments; swelling in hypotonic environments.
Contractile vacuole mechanisms in protists for osmoregulation.
Leaf Stomata and Guard Cell Function
Stomata: Pores for gas exchange; formed by guard cells.
Regulation Mechanism:
Water availability influences potassium ion movement, affecting guard cell turgor and pore opening.
Water Potential
Definition: Measurement of water's tendency to move, given by:
Factors Affecting Water Potential:
Solute addition decreases potential; pressure increases potential.
Conclusion
Emphasis on reviewing complex concepts and ensuring comprehension.
Encouragement to utilize learn-biology.com for additional resources and studying skills.
Introduction to Cells
Overview
Cells are fundamental units of life.
Mastery of cell structures and functions is essential for understanding biology.
Video structure outlined:
Introduction to cells
Why cells are small
Internal organization of cells (compartmentalization and organelles)
Cell parts and functions
Membrane structure and function
Osmosis
Additional resources for study (checklist at apbiosuccess.com/checklist)
Basic Structure and Parts of Cells
Definition of Cells
Cells are the basic unit of structure and function in every organism.
Surrounded by a membrane that divides cytoplasm from the external environment.
Contain genetic information in the form of DNA.
Systems exist to maintain and replicate cells and genetic information.
Gene Expression
DNA is transcribed into messenger RNA (mRNA).
mRNA is translated into proteins by ribosomes.
Proteins serve various functions, including serving as enzymes that control metabolism.
Prokaryotic vs. Eukaryotic Cells
Prokaryotic Cells
Characteristics:
Smaller and simpler.
No nucleus; circular chromosome.
Additional chromosomal pieces known as plasmids.
Domains:
Represented in Archaea and Bacteria.
Eukaryotic Cells
Characteristics:
Larger and more complex.
Defined nucleus; multiple linear chromosomes with associated proteins.
Presence of mitochondria and various membrane-bound organelles.
Cell Size and Surface Area to Volume Ratio
Importance of Cell Size
Smaller cells have a higher surface area to volume ratio than larger cells.
Calculation Example:
For a cell of 1 micron:
Surface Area = 6 1 1 = 6
Volume = 1 1 1 = 1
Ratio = 6:1
For a 10-micron cell:
Surface Area = 600
Volume = 1,000
Ratio = 0.6:1
Consequence of Size
Larger cells cannot efficiently diffuse nutrients or waste due to decreased surface area to volume ratios.
Increasing Surface Area in Organisms
Purpose of Increased Surface Area
Enhances diffusion capacity of molecules and heat.
Mechanisms:
Thin sheets of tissue (gills in fish).
Large, flat surfaces (ears of elephants).
Highly folded surfaces (mitochondrial membranes and villi in intestines).
Example of Size Evolution: Whales
Whales' Size Evolution
Warm-blooded mammals lose heat in cold ocean water.
Larger size reduces surface area to volume ratio, conserving heat and energy.
Natural selection favored larger body sizes for energy savings and enhanced fitness.
Absence of Small Marine Mammals
Small mammals (mouse-sized) struggle with thermal regulation.
High surface area to volume ratio leads to significant heat loss.
Adaptations of larger marine mammals (like sea otters) include dense fur for insulation.
Metabolism and Body Size
Definition of Metabolism
Sum total of chemical processes in an organism.
Metabolic Rate vs. Basal Metabolic Rate
Metabolic Rate: Energy expenditure over time.
Basal Metabolic Rate: Energy use at rest under comfortable conditions.
Measurement of Metabolic Rate
Through oxygen consumption, carbon dioxide production, or heat production.
Endotherms vs. Ectotherms
Endotherms: Generate body heat from metabolism.
Ectotherms: Body temperature conforms to ambient temperature.
Endotherms require more food but can maintain activity across various temperatures.
Body Size and Energy Requirements
Larger endotherms need to consume more food (e.g., an African elephant vs. a mouse).
Relative metabolic rate decreases as size increases.
Example Comparisons:
High heart rate and respiration = high energy needs in smaller mammals.
Larger mammals can sustain themselves with lower metabolic rates and longer food intake intervals.
Cellular Compartmentalization and Endomembrane System
Cell Compartmentalization
Definition: Internal division of a cell's space into sections (e.g. lysosomes).
Advantages: Allows distinct internal chemistries; increases surface area for processes.
Comparison:
Prokaryotic Cells: Fewer compartments, simpler structures; e.g. thylakoids in cyanobacteria.
Eukaryotic Cells: Highly compartmentalized with various organelles (e.g. lysosomes, mitochondria).
Endomembrane System
Definition: Dynamic system of interconnected membranes (includes nuclear membrane, ER, Golgi, and lysosomes).
Functionality: Constant membrane and material flow between compartments.
Origin of Eukaryotic Cells
All eukaryotes arose ~1.8 billion years ago from prokaryotes via endosymbiosis.
Evidence for Endosymbiosis:
Mitochondria and chloroplasts have circular DNA, replicate independently, resemble bacterial structures.
Description of Eukaryotic Cell Parts and Functions
Nucleus: Stores/protects genetic information in DNA; contains nucleolus for ribosome assembly; has nuclear pores for molecule passage.
Ribosomes: Composed of rRNA/proteins; sites of protein synthesis; can be free-floating or bound to the rough ER.
Mitochondria: Convert food energy into ATP; contain DNA, ribosomes; have an inner membrane with folds (increasing surface area).
Endoplasmic Reticulum (ER): Interconnected channels (Rough ER has ribosomes; Smooth ER synthesizes lipids and detoxifies).
Golgi Complex: Membrane-bound sacs modify, package proteins for export or delivery within the cell.
Lysosomes: Contain hydrolytic enzymes for digestion; recycle cellular components and execute apoptosis.
Cytoskeleton: A network of protein fibers providing shape and enabling cell movement.
Centrosomes/Centrioles: Assist with cell division by creating spindle fibers.
Plant Cell Structures
Central Vacuole: Large, stores water, molecules, waste products, essential for turgor pressure.
Chloroplasts: Endosymbiotic origins; involve in photosynthesis-producing carbohydrates.
Cell Wall: Composed of cellulose; prevents over-expansion due to osmotic pressure, provides structural support.
Membrane Structure and Function
Cell Membrane: Selectively permeable; separates cell contents from the environment.
Phospholipid Structure: Consists of hydrophilic heads and hydrophobic tails forming a bilayer stabilized by Van der Waals bonds.
Fluid Mosaic Model: Describes membrane structure; components move laterally, resembling a mosaic.
Protein Integration:
Transmembrane Proteins: Span the membrane; have hydrophobic core.
Integral Proteins: Span membrane with one side in the cytoplasm.
Peripheral Proteins: Attach to the membrane surface.
Transport Mechanisms Across Membranes
Diffusion: Movement of molecules from high to low concentration; passive transport requiring no energy.
Active Transport: Movement against concentration gradient requiring energy (ATP).
Bulk Transport: Includes endocytosis (ingestion) and exocytosis (expulsion).
Membrane Potential and Ion Transport
Definition: Electrical charge difference across a membrane, created through ion pump expenditure of energy.
Mechanism: E.g., proton pumps in mitochondria contributing to ATP synthesis and neuron activity.
Tonicity and Osmoregulation
Osmosis: Diffusion of water from low to high solute concentration.
Terms:
Hypotonic: More water, less solute.
Hypertonic: Less water, more solute.
Isotonic: Equal concentrations.
Effects on Cells:
Shrinkage in hypertonic environments; swelling in hypotonic environments.
Contractile vacuole mechanisms in protists for osmoregulation.
Leaf Stomata and Guard Cell Function
Stomata: Pores for gas exchange; formed by guard cells.
Regulation Mechanism:
Water availability influences potassium ion movement, affecting guard cell turgor and pore opening.
Water Potential
Definition: Measurement of water's tendency to move, given by:
Factors Affecting Water Potential:
Solute addition decreases potential; pressure increases potential.
Conclusion
Emphasis on reviewing complex concepts and ensuring comprehension.
Encouragement to utilize learn-biology.com for additional resources and studying skills.