Cells Flashcards
What do all cells have
All cells have a cell membrane (plasma membrane), cytoplasm, DNA (genetic material), and ribosomes
Cell membrane
primarily composed of a phospholipid bilayer, which acts as a double layer of lipid molecules with hydrophilic heads facing outward and hydrophobic tails facing inward, and embedded proteins that allow for selective transport of substances into and out of the cell
Phospholipid bilayer
embedded proteins, proteins for binding, adhering to adjacent cells, and communication
Function of cell membrane
a selective barrier, controlling what enters and exits a cell by acting as a gatekeeper, separating the cell’s internal environment from its surroundings while allowing necessary nutrients in and waste products out, maintaining the cell’s internal homeostasis through selective transport mechanisms facilitated by embedded proteins
Structure of phospholipid
fatty acids bound to glycerol; a phosphate group replaces one fatty acid
Prokaryotic cell components
- Cell membrane
- Nucleoid: region where DNA is located
- Cytoplasm: rest of the cell contents
- Ribosomes: sites of protein synthesis
Cell wall
rigid, outside the cell membrane, determines cell’s shape and provides support
Outer membrane
additional phospholipid membrane
found outside the peptidoglycan layer
Capsule
slimy layer of polysaccharides, protects cells
Flagella
appendage that helps cell swim
Pili
hairlike structures projecting from cell surface, help bacteria adhere to other cells
DNA function
to store the genetic information needed for an organism to develop, function, grow, and reproduce, found in the nucleus
Ribosomes
sites of protein synthesis
- Similar to prokaryotic ribosomes
- Consist of ribosomal RNA (rRNA) and >50 protein molecules
Smooth endoplasmic reticulum (SER)
no ribosomes
- Chemically modifies small molecules such as drugs, pesticides
-Site of glycogen degradation in
animal cells
- Synthesis of lipids, steroids
- Stores calcium ions
Rough endoplasmic reticulum (RER)
has ribosomes attached
- Newly made proteins enter RER lumen and are modified, folded, transported elsewhere
Golgi Apparatus
flattened sacs (cisternae) and small vesicles
- Receives proteins from RER and can modify them further
- Concentrates, packages, sorts of proteins
- In plant cells, synthesis of polysaccharides for cell wall
Lysosomes
contain digestive enzymes that hydrolyze macromolecules into monomers
Primary lysosomes
originate from Golgi apparatus
Secondary lysosomes
primary lysosomes fused with phagosomes
Peroxisomes
collect and break down toxic byproducts of
metabolism (e.g., H2 O2)
Nucleus structure and function
contains most of the DNA
- Usually largest organelle
- Site of DNA replication
- Site where gene transcription turned on/off
Endomembrane system
interconnected system of
membrane‐enclosed compartments
Endomembrane system is composed of
- Cell membrane
- Nuclear envelope
- ER
- Golgi apparatus
- Lysosomes
Mitochondria
convert chemical‐bond energy into a usable form ‐ energy‐rich ATP, has an outer and inner membrane, Inner membrane folds inward to form cristae – creates large
surface area for proteins involved in respiration, Mitochondrial matrix – contains enzymes, DNA, ribosomes, found in eukaryotic cells
Chloroplasts
site of photosynthesis; have double membrane, inner membrane forms thylakoids which contain chlorophyll and other pigments that harvest light energy, found in plant cells
Eukaryotic cells
appeared 1.5 billion years ago, Nucleus and endomembrane system: originated from inward folds of cell membrane in prokaryotes
Endosymbiosis theory
mitochondria and plastids arose
when one cell engulfed another
Endosymbiosis theory tenets
- Mitochondria originated as aerobic bacteria
- Chloroplasts originated as photosynthetic bacteria
- Genes/DNA moved and captured organisms couldn’t live on their own
Fluid mosaic model
describes general structure of biological
membranes, phospholipids form a bilayer, like a “lake” in which a variety of
proteins “float”
Membrane fluidity depends on
- Lipid composition: cholesterol and long‐chain, saturated fatty acids pack tightly, making membrane less fluid
- Temperature: fluidity decreases as temp. drops, some organisms change lipid content of membranes when cold, replacing saturated with unsaturated fatty acids and using fatty acids with shorter tails
Transmembrane proteins
extend all the way through phospholipid bilayer, contain one or more transmembrane domain
Transmembrane domain
on inner or outer side of bilayer, have specific functions
Selective permeablility
the ability of a membrane to control which substances can pass through it, while blocking others
Cell recognition
one cell specifically recognizes and
binds to another cell of a certain type
Cell adhesion
connection between two cells is
strengthened
Cell junctions and types
specialized structures that hold cells together, tight junctions, desmosomes, and gap junctions
Tight junctions
prevent substances from moving through
spaces between cells; help ensure directional movement of materials
Desmosomes
“spot welds”; materials can move around
in extracellular matrix, provides mechanical stability
Gap junctions
allow communication
Extracellular matrix (ECM)
heterogeneous mix of materials surrounding cells
Integrin
transmembrane protein that binds to matrix outside epithelial cells and to actin filaments inside cells
