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Chapter 6: A Tour of the Cell. Technology to study cells. light microscopes – pass visible light through specimen and lenses. magnification – ratio of image size to actual size. resolution – clarity of image; minimum distance between two distinguishable points.

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electron microscopes – focus beams of electrons through or onto specimen– resolution 100x better than light microscopes
Surface are to volume ratio:– limits cell size because as cells get bigger, their volume increases faster than their surface area
surface area important for transport of substances through the membrane
– surface area important for transport of substances through the membrane

microvilli in intestine

increases surface area for absorption

all cells have
All cells have:
  • cytosol– semifluid substance containing organelles and dissolved nutrients
  • plasma membrane – selective barrier
  • chromosomes – packaged DNA
  • ribosomes – make proteins
prokaryotic cells1
Prokaryotic Cells
  • smaller than eukaryotic cells
  • no membrane-bound organelles
  • no nucleus (nucleoid – region containing prokaryotic DNA)
  • small ribosomes
  • circular DNA
  • plasmids
nucleus contains dna
nucleus – contains DNA
  • nuclear envelope – double membrane that encloses nucleus
  • nuclear pores – holes in the nuclear envelope. Allow passage of large molecules.

chromosomes – made of chromatin, a complex of proteins and DNA

  • nucleolus – rRNA synthesized, ribosomes assembled
ribosomes synthesize proteins
ribosomes – synthesize proteins
  • made of ribosomal RNA (rRNA) and protein
  • cells that synthesize many proteins have many ribosomes
  • either free-floating in cytosol (make proteins for cell’s use) or bound to rough ER (make proteins for secretion)
endomembrane system
endomembrane system
  • more than half the total membrane of the cell
  • consists of membranous tubules and sacs (cisternae)
  • lumen – interior cavity of cisternae
smooth endoplasmic reticulum er
smooth endoplasmic reticulum (ER)
  • no bound ribosomes
  • synthesizes lipids (phospholipids, oils, steroids)
  • stores calcium ions, especially in muscles (important to muscle contraction)
enzymes detoxify drugs and poisons especially in the liver
Enzymes detoxify drugs and poisons, especially in the liver
  • add hydroxyl groups to drugs; makes them more soluble
  • drug tolerance due to proliferation of smooth ER in addicts; higher doses required to achieve the same effect
rough endoplasmic reticulum er
rough endoplasmic reticulum (ER)
  • has bound ribosomes
  • continuous with nuclear envelope

helps in synthesis of secretory proteins (proteins made for secretion), especially glycoproteins – proteins that have carbohydrates on them

  • adds carbohydrates to glycoproteins, sends them in transportvescicles (sacs of membrane) to Golgi

Also the membrane factory of cell; makes new membrane for itself that becomes vescicles; these eventually become part of cell membrane

golgi apparatus products of er modified stored and then shipped
Golgi apparatus – products of ER modified, stored and then shipped
  • flattened sacs (cisternae)
  • cis face – receiving side
  • trans face – shipping side

vescicles from ER fuse with cis face and empy contents into lumen of cisternae

  • products of ER modified in Golgi:

– modifies carbohydrates

– alters protein structure


Golgi makes some macromolecules

  • products transferred from one cisternae to another, eventually arrive at trans face.
  • products sorted and “addressed” for where they will go

vescicles bud off trans face and carry contents to cell membrane for export or to different parts of the cell

lysosomes digest
Lysosomes – digest
  • membrane sac of hydrolytic enzymes
  • digests molecules and worn-out cell parts (autophagy)
phagocytosis – food particle engulfed by cell and contained in vescicle– vescicle merges with lysosome and is digested
tay sachs
  • Lipids accumulate in nervous tissue
  • Degeneration of mental and physical abilities
  • Seizures, paralysis
  • Death before age 4

Cherry-red spot on retina identifies Tay-Sachs

  • membrane-bound sacs
  • central vacuole – in plants, storage for nutrients and wastes, water

– membrane: tonoplast


food vacuoles – formed by phagocytosis

  • contractile vacuoles – in protists, pump excess water out of cell
mitochondria make cell energy
Mitochondria – make cell energy
  • change molecular energy to cellular energy; cell respiration

double membrane

  • outer membrane is smooth
  • Inner membrane has folds called cristae
  • intermembrane space – between outer and inner membrane
  • mitochondrial matrix – lumen within the inner membrane
chloroplasts make carbohydrates
Chloroplasts – make carbohydrates
  • a plastid (other plastids are amyloplasts (store starch in plants) and chromoplasts (contain pigments that color fruit and flowers)
  • contain pigment chlorophyll

double membrane

– outer membrane smooth

– inner membrane is stacks of sacs called


  • a stack of thylakoids is a granum
  • fluid between granum and outer membrame is stroma
  • sac containing enzymes that transfer hydrogen to oxygen, producing H2O2
  • digestion of fats, detoxification of alcohol
  • not part of endomembrane system (lysosomes are)
  • support, maintain cell shape
  • cell motility (movement): both movement of whole cell and parts of cell within.
  • motor proteins – help cytoskeleton accomplish movement
  • hollow tubes of 13 columns of tubulindimers
  • 25 nm
  • -tubulin and -tubulin
  • cell shape (reists compression), cilia and flagella, move chromosomes during cell division, organelle movement
microfilaments actin filaments
Microfilaments (actin filaments)
  • 2 intertwined strands of actin
  • 7 nm
  • cell shape (resist force), muscle contraction, cytoplasmic streaming, pseudopodia in amoeboid movement
intermediate filaments
Intermediate filaments
  • thick cables of fibrous protein
  • 8-12 nm
  • fibrous Keratin protein
  • cell shape (resist force), anchorage of nucleus and organelles
centosomes and centrioles
Centosomes and centrioles
  • centrosome – region near nucleus where microtubules grow out from
  • centrioles – in animals, 9 sets of triplet microtubules that help organize mitotic spindle during cell division
cillia and flagella
Cillia and flagella
  • 9 + 2 arrangement of microtubules
  • dynein arms are motor proteins
flagella – a tail-like structure for cellular locomotion or moving liquid past cell– made of microtubules

Dynein arms bend cilia and flagella

  • Dynein “walking”: arms of one microtubule grip adjacent doublet, push it up, release, then repeat
basal body where cilium or flagellum is anchored to cell
basal body – where cilium or flagellum is anchored to cell
  • – 9 sets of triplet microtubules (9 x 3)
  • – a basal body of a sperm flagellum enters egg and becomes a centriole
cell wall
cell wall
  • made of cellulose microfibrils and proteins. Protects, maintains shape, prevents too much water
  • also in prokaryotes, fungi and some protists
  • primary cell wall – young cell wall. Thin and flexible
  • secondary cell well – in woody plants. Grown between membrane and primary wall.

middle lamella – between primary cell walls of adjacent cells. Rich in pectins (sticky polysaccharides). Glues cells together.

  • plasmodesmata
animal extracellular matrix ecm
Animal Extracellular Matrix (ECM)
  • Mostly glycoproteins; mainly collagen fibers
  • Collagen embedded in a network of proteoglycans

fibronectin – another glycoprotein in the ECM that binds integrins on cell membraneintegrins – proteins that span the cell membrane and transmit info on changes outside the cell to the cytoplasm


Changes in ECM my trigger changes in cells.

  • Integrins help relay signals to and from cells
  • Play role in coordinating behavior of all cells in a tissue.
intercellular junctions
Intercellular junctions
  • Plasmodesmata (plants) – channels made by perforation in cell walls. Cytosol, water and nutrients passes through them, linking cells
  • tight junctions (animals) – membranes of cells tightly pressed together, bound by proteins. Prevents leakage.

desmosomes(animals) – fasten cells together into a strong sheet. Like rivets.

  • gap junctions (animals) – channels between cells through which flow ions, sugars, other molecules. Useful in cell communication.