Sept 8th Flashcards
BIOLOGY 201 – LECTURE NOTES
INTRODUCTION TO CELLS AND CELL STRUCTURE
WHAT IS LIFE?
Living organisms have several important characteristics:
Exchange materials and energy with their environment
Grow and develop
Reproduce
Respond to changes in their environment
Carry out metabolism
Eventually die
Life is considered an emergent property of organized molecules.
Emergent property = a characteristic that appears when smaller components interact and become organized into a larger system.
Example:
Individual molecules are not "alive," but when organized into cells, they can produce the characteristics of life.
CRYSTALS VS. LIVING ORGANISMS
Crystals:
Can grow
Can become larger over time
Are made of organized molecules
However, crystals are NOT considered alive because they cannot:
Reproduce independently
Carry out metabolism
Respond to their environment in the way living organisms do
VIRUSES:
Viruses are sometimes considered a "gray area" between living and non-living.
They contain genetic material and can reproduce, but they cannot reproduce independently or carry out metabolism on their own.
Therefore, viruses are generally NOT classified as living organisms.
CELLS = BASIC UNIT OF LIFE
The cell is the fundamental unit of all known life.
All living organisms are made of one or more cells.
Two major types of cells:
Prokaryotic cells
Eukaryotic cells
PROKARYOTIC CELLS
Prokaryotic cells are generally simpler and smaller than eukaryotic cells.
Examples:
Bacteria
Archaea
Important characteristics:
No nucleus
DNA is located in a region called the nucleoid
No membrane-bound organelles
Usually unicellular
Generally smaller than eukaryotic cells
EUKARYOTIC CELLS
Eukaryotic cells are generally larger and more complex.
Examples:
Animals
Plants
Fungi
Protists
Important characteristics:
Have a nucleus
DNA is contained inside the nucleus
Have membrane-bound organelles
Can be unicellular or multicellular
Generally larger than prokaryotic cells
UNICELLULAR VS. MULTICELLULAR
UNICELLULAR:
Made of one cell
The single cell performs all necessary functions
Examples:
Many bacteria
Some protists
Some fungi
MULTICELLULAR:
Made of many cells
Different cells can specialize for different functions
Examples:
Humans
Plants
Most animals
CELL SIZE
Cells are generally very small.
Cells are measured using units such as:
Micrometer (µm) = 10⁻⁶ m
Nanometer (nm) = 10⁻⁹ m
Microscopes are used to observe cells because most cells are too small to see clearly with the naked eye.
SURFACE-TO-VOLUME RATIO
One major reason cells are small is their surface-to-volume ratio.
Surface area = area available for exchanging materials with the environment.
Volume = amount of space inside the cell.
As a cell gets larger:
Volume increases faster than surface area.
Surface-to-volume ratio decreases.
It becomes harder for the cell to exchange materials efficiently.
Therefore, cells generally remain small to maintain a high surface-to-volume ratio.
HIGH-YIELD:
Small cell → high surface-to-volume ratio → efficient exchange of materials
Large cell → low surface-to-volume ratio → less efficient exchange
BASIC STRUCTURE OF A PROKARYOTIC CELL
Important structures:
CYTOSOL
Fluid portion inside the cell
Many chemical reactions occur here
PLASMA MEMBRANE
Surrounds the cell
Controls what enters and leaves the cell
Made primarily of phospholipids and proteins
RIBOSOMES
Make proteins
Found in both prokaryotic and eukaryotic cells
NUCLEOID
Region containing the cell's DNA
NOT surrounded by a membrane
Found in prokaryotic cells
PHOSPHOLIPID BILAYER
The plasma membrane is mainly composed of a phospholipid bilayer.
Phospholipid = molecule with:
A hydrophilic (water-loving) head
Hydrophobic (water-fearing) tails
In the membrane:
Heads face toward water.
Tails face away from water and toward each other.
This creates a phospholipid bilayer.
The membrane is selectively permeable (semipermeable).
This means it allows some substances to cross more easily than others.
OSMOSIS
Osmosis = movement of water across a selectively permeable membrane.
Water moves from an area of:
LOW SOLUTE CONCENTRATION
→
HIGH SOLUTE CONCENTRATION
The movement continues until equilibrium is reached.
AQUAPORINS:
Specialized membrane proteins
Allow water to cross the membrane quickly
Are a type of channel protein
MEMBRANE FLUIDITY
The plasma membrane is NOT rigid.
It is fluid and flexible.
Phospholipids can move within the membrane.
This is sometimes described as the:
"Fluid mosaic model"
Fluid = molecules can move within the membrane.
Mosaic = many different molecules, including proteins, are embedded throughout the membrane.
MEMBRANE TRANSPORT PROTEINS
Membrane proteins help substances move across the plasma membrane.
Four important types:
Channel proteins
Gated channel proteins
Carrier proteins
Active transport proteins
CHANNEL PROTEINS:
Form a passage through the membrane
Allow specific substances to move through
GATED CHANNELS:
Open or close in response to a signal
Control when substances can pass
CARRIER PROTEINS:
Bind to a specific substance
Change shape to move the substance across the membrane
ACTIVE TRANSPORT PROTEINS:
Use energy to move substances
Can move substances against their concentration gradient
PASSIVE TRANSPORT / FACILITATED DIFFUSION
Passive transport does NOT require cellular energy.
Substances move down their concentration gradient:
HIGH concentration
→
LOW concentration
Facilitated diffusion uses membrane proteins to help substances cross the membrane.
Important:
Facilitated diffusion = passive transport
No ATP is required.
ACTIVE TRANSPORT
Active transport requires energy.
Substances can be moved against their concentration gradient:
LOW concentration
→
HIGH concentration
Energy is usually supplied by ATP.
ATP → ADP + energy
The energy released can be used by transport proteins to move substances across the membrane.
OPTIONAL STRUCTURES IN BACTERIA
Some prokaryotic cells have additional structures.
CELL WALL
Provides structural support
Helps protect the cell
FLAGELLUM
Used for movement
Long, whip-like structure
FLAGELLA = plural of flagellum
CAPSULE / SLIME SHEATH
Protective outer layer
Can help bacteria attach to surfaces
PLASMIDS
Small circular pieces of DNA
Separate from the main bacterial chromosome
Can contain useful genes
THYLAKOIDS
Membrane structures found in some photosynthetic bacteria
Involved in photosynthesis
EUKARYOTIC CELL STRUCTURES
Eukaryotic cells contain many structures that are also found in prokaryotic cells:
Plasma membrane
Cytosol
Ribosomes
DNA
However, eukaryotic cells also contain membrane-bound organelles.
NUCLEUS
The nucleus contains the cell's DNA.
The nucleus is surrounded by the:
NUCLEAR ENVELOPE
The nuclear envelope:
Surrounds the nucleus
Separates DNA from the cytoplasm
Contains nuclear pores
NUCLEAR PORES:
Allow substances to move between the nucleus and cytoplasm
CHROMATIN
Chromatin = DNA associated with proteins inside the nucleus.
When a cell is not dividing, DNA exists mainly as chromatin.
Chromatin can condense into chromosomes during cell division.
NUCLEOLUS
The nucleolus is a region inside the nucleus.
Main function:
Produces components needed to make ribosomes
Important:
Nucleolus ≠ nucleus
Nucleus = contains DNA
Nucleolus = produces ribosome components
COMPARTMENTALIZATION
Eukaryotic cells are compartmentalized.
Compartmentalization = dividing the cell into separate regions using membranes.
This allows different chemical reactions to occur in different parts of the cell.
Example:
DNA is kept inside the nucleus.
Other processes occur in the cytoplasm and organelles.
This makes eukaryotic cells more complex and efficient.
SMOOTH ENDOPLASMIC RETICULUM
The smooth endoplasmic reticulum (smooth ER) is a membrane-bound organelle.
Functions include:
Lipid production
Detoxification
Storage of certain substances
It is called "smooth" because it does not have ribosomes attached to its surface.
ROUGH ER:
Has ribosomes attached
Involved in protein production
SMOOTH ER:
No ribosomes attached
Involved mainly in lipid-related functions
CILIA AND FLAGELLA
Some eukaryotic cells have structures used for movement.
FLAGELLUM:
Usually longer
Usually fewer in number
Helps move the cell
CILIA:
Shorter
Usually present in large numbers
Can move substances across the surface of a cell
Singular:
Flagellum
Cilium
Plural:
Flagella
Cilia
PROKARYOTIC VS. EUKARYOTIC CELLS
PROKARYOTIC:
Smaller
Simpler
No nucleus
DNA in nucleoid
No membrane-bound organelles
Usually unicellular
Includes bacteria and archaea
EUKARYOTIC:
Larger
More complex
Has nucleus
DNA inside nucleus
Has membrane-bound organelles
Can be unicellular or multicellular
Includes animals, plants, fungi, and protists
HIGH-YIELD EXAM CONCEPTS
Know these especially well:
Cell = fundamental unit of life
Prokaryotic cells: • No nucleus • DNA in nucleoid • No membrane-bound organelles
Eukaryotic cells: • Have a nucleus • Have membrane-bound organelles
Ribosomes make proteins.
Plasma membrane controls movement into and out of the cell.
Phospholipid bilayer: • Hydrophilic heads face water • Hydrophobic tails face inward
Osmosis = movement of water across a selectively permeable membrane.
Aquaporins = water channel proteins.
Passive transport: • Does not require ATP • Moves down concentration gradient
Active transport: • Requires energy • Can move substances against concentration gradient
ATP provides energy for cellular processes.
Surface-to-volume ratio explains why cells are generally small.
Nucleus contains DNA.
Nucleolus produces ribosome components.
Chromatin = DNA + associated proteins.
Compartmentalization allows different processes to occur in separate parts of the cell.
ONE-MINUTE REVIEW
Life:
Exchange with environment
Growth
Reproduction
Response
Metabolism
Death
Cells:
Basic unit of life
Prokaryotic = no nucleus
Eukaryotic = nucleus
Membrane:
Phospholipid bilayer
Selectively permeable
Fluid mosaic model
Transport:
Passive = no energy, high → low
Active = energy required, can move low → high
Osmosis = water movement
Aquaporins = water channels
Prokaryotic structures:
Cytosol
Plasma membrane
Ribosomes
Nucleoid
Eukaryotic structures:
Nucleus
Nuclear envelope
Nuclear pores
Nucleolus
Chromatin
Membrane-bound organelles
KEY TERMS TO MEMORIZE
Prokaryotic
Eukaryotic
Cytosol
Plasma membrane
Phospholipid bilayer
Ribosome
Nucleoid
Nucleus
Nuclear envelope
Nuclear pore
Nucleolus
Chromatin
Compartmentalization
Osmosis
Aquaporin
Passive transport
Facilitated diffusion
Active transport
ATP
ADP
Surface-to-volume ratio
Flagellum
Flagella
Cilium
Cilia
Smooth endoplasmic reticulum
Plasmid
Cell wall
Capsule
Thylakoid