AP Biology Unit 2: Cell Structure and Function

Cell Theory

All organisms are composed of one or more cells, and all cells arise from pre-existing cells

Prokaryotic cells include

Bacteria and archaea

Prokaryotic Cell

No nucleus, lack membrane-bound organelles, less complex, and smaller

Eukaryotic cells include

Plants, animals, fungi, and protists

Eukaryotic Cells

Cells that contain a nucleus and membrane-bound organelles and are generally larger and more complex

Ribosome structure:

Made up of two subunits, protein and rRNa

Ribosome function:

Produces proteins based on DNA/RNA sequence

Plasma (cell) membrane structure:

Phospholipid bilayer with embedded proteins

Plasma (cell) membrane function:

Regulates the entry and exit of substances in and out of the cell

Membrane protiens

Aid in regulation

Cytosol structure:

Semifluid solution composed of water and inorganic and organic molecules

Cytosol function:

Hold other organelles in place and the enzymes help aid in chemical reactions

Cytoplasm

The material within a cell membrane, excluding the nucleus, that includes cytosol and organelles

All cell types have a…

Plasma membrane, ribosome, and cytoplasm

Endosymbiotic Theory

Mitochondria and chloroplasts are membrane bound organelles that were engulfed by Eukaryotic cells billions of years ago

Evidence of Endosymbiotic theory

Mitochondira DNA: Circular DNA resembles prokaryotic cells

Evidence of Endosymbiotic theory

Mitochondria/Chloroplast Membrane: Outer membrane from the eukaryotic cell and inner membrane resembling prokaryotic membranes.

Evidence of Endosymbiotic theory

Ribosomes in the Mitochondria: resemble those of prokaryotes

Evidence of Endosymbiotic theory

Mitochondria reproduce similarly as both divide in an asexual fashion similar to binary fission of bacteria

Nucleus structure:

Circular, double-membrane structure found near the center of the cell

Nucleus function:

Contains the cell's genetic material (DNA) and regulates gene expression

Nucleolus

A dense, spherical structure within the nucleus responsible for ribosome production

Nuclear envelope

Double membrane that surrounds the nucleus, separating its contents from the cytoplasm

Nuclear pores

Protein complexes that allow the transport of molecules between the nucleus and cytoplasm

Endomembrane system contains the…

Endoplasmic reticulum, golgi body, vesicles, and lysosomes/peroxisomes

Endoplasmic Reticulum (ER)

Complicated structure of membrane channels. Physically connected to the nuclear envelope

Rough ER structure:

Membrane connected to outer nuclear envelope. Ribosomes attached to its cytoplasmic surface, giving it a "rough" appearance

Rough ER function:

Produces proteins, folds extracellular proteins inside lumen

Smooth ER structure:

Connected to the nuclear envelope and rough ER but lacks ribosomes, resulting in a smooth appearance.

Smooth ER function:

Produces lipids, breaks molecules down, and sends vesicles to golgi body

Vesicle structure:

Small, membrane-bound sacs that transport materials within the cell

Vesicle function:

Transport materials around the cell

Golgi body structure:

Stack of curved saccules (flattened vesicles)

Golgi body function:

Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles

Extracellular proteins

Proteins from the ER are released outside the cell and play roles in cell signaling, structural support, and communication

Membrane bound organelle

Any organelle with its own membrane (phospholipid bilayer)

Lysosome structure:

Membrane bound vesicle, produced by Golgi apparatus, contain digestive enzymes

Lysosome function:

Break down non-functioning organelles, invading pathogens, and more

Peroxisome structure:

Membrane-bound organelles containing enzymes

Peroxisome function:

Help break down fatty acids and dangerous chemicals

Peroxisomes

Oxidases in cell convert free radical H and O to hydrogen peroxide (H₂O₂)

Peroxisomes

Catalases in cell convert hydrogen peroxide into water (H₂O)

Vacuoles strucuture:

Membrane sacs, that store substances such as water and food

Vacuoles function:

Storage of substances such as nutrients, waste products, and water (1 large in plants/ many in animal)

Chloroplast structure:

Membrane-bound organelles containing chlorophyll, filled with pigments

Chloroplast function:

Location of photosynthesis, uses solar energy to synthesize carbohydrates

Mitochondria structure:

Double membrane-bound organelles with inner folds called cristae

Mitochondria function:

Responsible for producing ATP through cellular respiration

Plant organelles:

Large central vacuole, chloroplasts, mitochondria, rectangular shape and cell wall

Animal organelles:

Many small vacuoles, mitochondria, lysosomes, circular or irregular shaped cells without a cell wall

Microfilament structure:

Actin fibers consisting of two chains of actin monomers

Microfilament function:

Used for structural support and movement of the cell

Intermediate filament structure:

Rope-like protien structure

Intermediate filament function:

Supports nuclear envelope and plasma membrane

Microtubule structure:

Small hallow cylinders compose of protien

Microtubule function:

Helps with structure of a cell, creates track for motor proteins, helps with cell division

Anchor proteins

Attachment points for cytoskeleton and extracellular matrix

Extracellular Matrix (ECM) structure:

Meshwork of protiens and polyssacharides located on outside of cell membrane

Extracellular Matrix (ECM) function:

Communication, between cells, connected to cytoskeleton through transmembrane protiens, and holds tissues together

Integrin

Trabsnmembrane proteins that facilitate communication between the extracellular matrix and the cytoskeleton

Desmosomes

Connections that hold cells together. Made through cytoskeleton

Desmosomes example:

Holds cells together where tissues stretch (heart, stomach, skin, intestines)

Tight junctions

Membrane proteins attach to each other, creates watertight surface

Tight junctions example:

Watertight seal or glue (bladder, kidney cells)

Gap junction

Location where water and ions can travel through. Helps with communication

Gap junction function:

Resembles a tunnel (Heart, nerve cells)

Passive transport

The movement of molecules across a cell membrane without energy input, moving down their concentration gradient

Diffusion

The process by which molecules spread from areas of high concentration to areas of low concentration, often through a semi-permeable membrane

Facilitated diffusion

Transport of molecules across the membrane through channel/carrier protiens

Osmosis

The diffusion of water molecules across a semi-permeable membrane, moving from areas of low solute concentration to high solute concentration

Hypotonic

A solution that has a lower concentration of solutes compared to another solution, causing cells to swell as water enters

Hypertonic

A solution that has a higher concentration of solutes compared to another solution, causing cells to shrink as water exits

Isotonic

A solution that has an equal concentration of solutes compared to another solution, resulting in no net movement of water into or out of cells

Plasmolysis

When the cytoplasm of a cell shrinks due to osmosis

Active transport

Transporting molecules up the concentration gradient which requires energy

Protein pumps

Membrane proteins use ATP to pump molecules against concentration gradient

Protein pump example:

Sodium potassium pump

Endocytosis

Portion of the plasma membrane fuses around substance that enters the cell

Endocytosis example:

Chlosteral uptake

Exocytosis

An intracellular process where vesicles fuse with the plasma membrane to release contents outside the cell

Exocytosis example:

Neurotransmitters

Cell communication

All multicellular organisms must communicate and cooperate to maintain homeostasis

Cells communicate by…

Sending/recieving signals then convert the signals into a response

Autocrine

Occurs when a cell targets itself

Autocrine analogy:

Leaving yourself a reminder to complete something later

Cell-to-cell (juxtracrine)

Membranes that are touching have membrane protiens that help with communication

Cell-to-cell (juxtracrine) analogy:

Paper note. You can pass the note to the person sitting next to you

Short distance

Communication of molecules, creates response in other cells (no cpmmection)

Short distance (paracrine)

Cell secrets signaling molecules to near by cells

Short distance (synaptic)

Stimulation of nerve cells by neurotransmitters

Short distance analogy:

Like a snapchat, goes to the receiver and then goes away

Long distance

(Endocrine) signaling involves hormones released into the bloodstream that can affect distant target cells.

Long distance analogy:

Facebook post. Message goes to everyone however how people react is up to them

Ligand

Chemical molecules that bond with protiens. Can’t pass through membrane

Receptor

Membrane protien that bonds with ligands

Secondary messenger

Internal protiens that relay message

Reception

The ligand binds to the specific receptor protein, which will change its shape

Transduction

Receptions sets off a relay team of communication protiens in the cell; second messengers carry the original exteriror signal to the inside of the cell

Response

The cell will respond to the signal as directed (e.g., make a protein, produce more energy, enter mitosis, etc)

Signal pathways

The same signal can trigger different responses depending on the recieving cell