Chapter 4: Cell Structure and Function Flashcards
What are the parts of the cell theory?
- all living things are made of cells
- cells are the basic unit of structure and function
- cells come from existing cells
Why can only some cells be seen with a light microscope?
there is a minimum resolution, which is around the size of small bacteria (~200 nm) to see the cell
What parts of cells can be seen with a light microscope?
nucleus/chromosomes in dividing cells/central vacuole/NOT other organelles
Why is an electron microscope helpful to us?
- electromagnets focus beam of electrons
- better resolution than light microscope
- can only observe organelles in DEAD cells
How does a transmission electron microscope work, and why is it helpful?
- thin sections of specimens are stained with heavy metals
- can see cell organelles
How does a scanning electron microscope work, and why is it helpful to us?
- sample surface is covered with a thin gold film
- study surface structures of cells
- image looks 3D
Cell Fractionation
uses an ultracentrifuge to separate major organelles to study
What are characteristics of all cells?
- surrounded by a cell membrane
- contain semifluid substance within membrane (cytosol)
- have organelles suspended in semi-fluid substance called the cytoplasm
- contain chromosomes (DNA)
- have ribosomes
Characteristics and examples of prokaryotes
- bacteria
- no nuclear membrane
- no membrane bound organelles
- DNA is in nucleoid region
Characteristics and examples of eukaryotes
- plants, animals, fungi, protists
- DNA surrounded by nuclear envelope
- contains membrane bound organelles
How big are most bacteria?
1-10 um (mirons)
How big are most eukaryotic cells?
10-100 um (microns)
Why is there a size limit on cells?
- need an upper limit due to metabolic requirements
- if a cell is too big it cannot transport food, oxygen, and waste fast enough for its needs
Relationship between surface area and volume of a cell
as cells increase in size, volume increases faster than the surface area (SA / volume ration decreases)
How do large organisms adapt to their large size?
- have more cells, not bigger cells
- have microvilli on cells to increase surface area
Structure and function of internal membranes in eukaryotes
- mainly made of phospholipids and proteins
- divide cell into various compartments
- take part in metabolism
- membrane surfaces compartmentalize
Structure and function of plasma membrane
- phospholipid bilayer (polar/hydrophilic heads face out and nonpolar/hydrophobic tails face in)
- selectively permeable because of the hydrophobic tails (some molecules can go through, others cannot)
Structure and function of the nuclear envelope
- contains genes in eukaryotes
- surrounded by a double membrane
- has nuclear pores lined by proteins to regulate passage of molecules
- nuclear side of envelope is lined with protein filaments (nuclear lamina) to maintain shape
- contains chromatin fibers = DNA + histone proteins
- chromatin wraps into chromosomes during cell division
- has nucleolus, which is the site of ribosome (rRNA) production
Structure and function of ribosomes
- made of proteins and rRNA
- synthesize proteins
- free ribosomes = make cytosol proteins
- bound ribosomes on ER or nuclear envelope = make proteins for cell membranes or export
Structure and function of endomembrane system
- continuous or connect with transfer of membrane sacs (vesicles)
- includes nuclear envelope, ER, Golgi body, lysosomes, vacuoles, plasma membrane
Structure and function of endoplasmic reticulum
- membranous tubules filled with internal fluid filled spaces (cisternae)
- continuous with nuclear envelope
Structure and function of rough ER
- ribosomes are attached
- many of them in cells that secrete proteins
- proteins synthesized on ribosomes, and folded into 3D shape in cisternal space
- secretory proteins are put into vesicles and sent to Golgi body
- makes membranes/phospholipids
- as ER grows, vesicles move membranes
Structure and function of smooth ER
- does not have ribosomes
- has many enzymes to help synthesize oils, steroids, and phospholipids (sex hormones, adrenal steroids)
- in liver: helps break down toxins
- in muscle: stores Ca+ ions to regulate muscle contraction
- frequent drug use leads to increase of SER & why it can lead to liver damage (CIRRHOSIS)
Structure and function of golgi apparatus
- flattened membranous sacs = cisternae
- cell “UPS” - manufacture, warehouse, sort, ship
- has direction
- cis face facing ER = receiving side
- trans side = shipping side where
transport vesicle buds off - extensive in secretory cells
- can manufacture own macromolecules (amylopectin)
- phosphate groups act as zip codes and can help identify product’s destination
Structure and function of lysosomes
- found in animal cells
- membrane bound sac of hydrolytic enzymes –> can hydrolyze food, whole cells, damaged cell parts
- example of compartmentalization
- enzymes work best at pH of 5
- H+ ions are pumped from cytosol to
lysosome - massive rupture of lysosomes can destroy a cell by “
Structure and function of lysosomes
- found in animal cells
- membrane bound sac of hydrolytic enzymes –> can hydrolyze food, whole cells, damaged cell parts
- example of compartmentalization
- enzymes work best at pH of 5
- H+ ions are pumped from cytosol to
lysosome - massive rupture of lysosomes can destroy a cell by “
Structure of lysosomes and how they work
- found in animal cells
- membrane bound sac of hydrolytic enzymes –> can hydrolyze food, whole cells, damaged cell parts
- example of compartmentalization
- enzymes work best at pH of 5
- H+ ions are pumped from cytosol to
lysosome
- massive rupture of lysosomes can
destroy a cell by “self-digestion”
(autophagy)
Function/purpose of lysosomes
- digestion of food in unicellular organisms
- recycle cell’s organelles and macromolecules
- programmed cell death (apoptosis)
- embryonic development (form fingers,
lose tail)
- cells that are damaged get signal to self-
destruct
What can a malfunction of lysosomes lead to?
- Tay-Sacs = genetic disorder
- don’t have lysosomal enzymes to break down lipids
- accumulation of lipids in the brain may lead to seizures, death, blindness, etc
Structure and formation of vacuoles
- vesicles and vacuoles (larger) = membrane-bound sacs
- food vacuoles form by phagocytosis and fuse with lysosomes
- surrounded by membrane = tonoplast
Function of vacuoles
- contractile vacuoles in freshwater protists = pump out excess water to maintain balance
- large central vacuole in many plant cells
- stockpile proteins/inorganic compounds
- dispose of metabolic byproducts
- contain pigments
- store defensive compounds to defend plants against herbivores
- large vacuole reduces area of cytosol –> SA/volume ratio increases
- water storage makes plants turgid
Structure and function of peroxisomes
- single membrane around it
- made of proteins and lipids in cytosol
- breaks down fatty acids and transports them to mitochondria, then mito uses it them for ceullular respiration
- detoxifies alcohol
- peroxisomes in seeds (glyoxysomes) convert fatty acids into sugars
- have enzymes that transfer hydrogen from substrates to oxygen
- makes hydrogen peroxide
- contains catalase to convert H2O2 –>
H20 + O2
Structure of mitochondria
- not part of endomembrane system
- membrane proteins are made by free ribosomes and ribosomes in mitochondria
- semi-autonomous = grow/reproduce on their own
- mobile; move on cytoskeleton tracks
- double membrane makes internal compartments
- smooth outer membrane/inner membrane separated by intermembrane space
- folded inner membrane (cristae) increases surface area for chemical reactions
- fluid filled space enclosed by inner membrane (matrix)
- has DNA, ribosomes, enzymes
Function of mitochondria
- site of cellular respiration
- breaks down sugars, fats, fuels in presence of oxygen
- generates ATP
- cells with high energy needs have many mito
Structure of chloroplasts
- not in endomembrane system
- plastid found in leaves/green organs
- membrane proteins made by ribosomes and those in chloroplasts
- semi-autonomous = grow/reproduce on their own
- mobile; move on cytoskeleton tracks
- double-membrane creates internal compartments
- fluid filled space inside = stroma (has
DNA, ribosomes, etc)
- granum = stacks of thylakoid sacs (trap
light energy)
Function of chloroplasts
- site of photosynthesis
- convert solar energy to chemical energy
- synthesize new organic compounds like sugars from CO2 and H2O
Examples of plastids
- amyloplast = colorless plastid that store starch in roots and tubers
- chromoplast = store color pigments for fruits and flowers
What is the endosymbiosis theory?
- engulfed prokaryotes shared symbiotic relationship with the host cell
- one gives energy, one gives raw
materials/protection - origin of mitochondria and chloroplasts
What evidence shows that chloroplasts and mitochondria correlate with the endosymbiosis theory?
- only organelles besides nucleus with own DNA and double membranes
- have single, circular naked (no histones) DNA
- inner membranes have enzymes and transport systems like bacterial plasma membranes
- replicate independently of nucleus - binary fission
- ribosome size, nucleotide sequence, sensitivity to some antibiotics is similar to bacterial ribosomes
Structure and function of centrioles
- only in dividing animal cells
- made of microtubules in pattern of 9 triplets
- found inside centrosome, move to poles during cell division
Structure and function of the cytoskeleton
- network of fibers that extend throughout the cytoplasm
- provides support and maintains cell shape
- anchorage for many organelles and
cytosolic enzymes
- dismantled in one part and reassembled
in another part
- helps with cell motility
Tubulin microtubules (type of cytoskeleton fiber)
- thickest
- hollow tube = dimer, made of protein subunits; change length by add/remove dimer
- make tracks for motor proteins to go to
organelles/vesicles
- separate chromosomes during cell
division - centrosomes = microtubule organizing region in many cells
- in animal cells it contains centrioles
Actin microfilaments (type of cytoskeleton fiber)
- thinnest
- made of protein actin in double twisted chain
- support network inside membrane
- support cell shape
- interact with myosin filaments for muscle contraction
- cleavage furrow in cell division: amoeboid movement (pseudopodia) & cytoplasmic streaming (plant cells)
Intermediate filaments (type of cytoskeleton fiber)
- middle size
- more permanent framework/anchor cell organelles in place
- made of keratin proteins
What are motor proteins?
- require ATP
- go along cytoskeleton tracks to move to organelles, vesicles, chromosomes
- myosin heads interact with actin for muscle contraction
- dynein arms interact with tubulin to move cilia and flagella
Structure and function of eukaryotic cilia and flagella
- extend from cell surface
- surrounded by plasma membrane sheath
- anchored in cell by basal body (like
centriole) - made of microtubules in a 9+2 pattern
- 9 doublets in a ring around pair in center
- flexible protein wheels connect
microtubule doublets and center
- motor proteins connect outer doublets - movement of dynein arms causes bending and moving
Differences between cilia and flagella
- differ in length, size, beating pattern
cilia:
- short (2-20 um), long, large numbers
- in windpipe to sweep mucus
flagella:
- long (10-200 um), one or few
- single protein filament (not 9+2), no outer membrane sheath
Structure and function of cell wall
- found in plants, some prokaryotes, fungi, protists
- protect, support, keep shape
- microfibrils of cellulose are embedded in a matrix of proteins and polysaccharides
- middle lamella/polysaccharides hold cells/secondary cell walls together
- plasmodesmata (channels btwn adjacent cells) which connect cytosol –> water/small solutes/proteins can pass freely from cell to cell
Structure and function of animal cell’s extraceullular matrix
- outside of plasma membrane
- made of glycoproteins secreted by the cell
- strengthens tissues
- cell signaling, can turn on genes, modify biochemical activity, coordinate behavior of cells in a tissue
Tight junctions (intercellular links)
- membranes are fused
- form continuous seal
- prevents leakage of extracellular fluids
Desmosomes (intercellular links; anchoring junctions)
- fasten cells together in strong sheets
- keratin protein anchors to cytoplasm
Gap junctions (intercellular links; communication junctions)
- similar to plasmodesmata in plants
- cytoplasmic channels between adjacent cells
- special proteins surround these pores –> allow ions, sugars, amino acids, etc, to go through
- help facilitate chemical communication in embryos during developmental stage
