Cell Structure and Function

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Cell Structure and Function
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ANATOMY AND PHYSIOLOGY I LECTURE NOTES

• CELL BIOLOGY
• CELL THEORY
• Schleiden and Schwann (1830)
• all living things are composed of cells

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CELLS IN HUMANS

• size variation
• red blood cells ( 7.5 micrometers)
• female 'egg' cell 300 micrometer
• structural variations
• muscle cells-very long
• nervous cells- conduct impulses
• red blood cells- transport gases

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THE TYPICAL CELL

• CELL STRUCTURES AND FUNCTIONS
• Nucleus-
• nuclear membrane has nuclear pores
• double layered
• function of nucleus
• contains genetic material of cell
• controls all functions in cell

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CELL STRUCTURES AND FUNCTIONS

• nucleolus
• contains RNA
• site of synthesis of mRNA, rRNA, tRNA

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Cell membrane ( plasma membrane)

• phospholipid bilayer
• cholesterol
• found in the hydrophobic region of phospholipid
  bilayer
• glycolipids
• lipid portion faces to outside

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Cell membrane, cont.

• membrane proteins
• channels
• enzymes
• glycoproteins
• proteins with added carbohydrates

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fluid mosaic model of cell membranes

• movement of proteins and glycoproteins within in
  the membrane (pattern pieces)
• movement of phospholipids , into and out of the
  membrane and within membrane ( background pieces)

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ESSENTIAL FUNCTIONS OF CELL MEMBRANES

• maintains integrity of cell or organelle
• transports water soluble molecules
• contains receptors for hormones

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FUNCTIONS OF CELL MEMBRANES

• regulation of metabolic reactions ( membrane
  enzymes)
• support and shape of cell ( cytoskeleton)
• identification of cells or organelles (
  glycoprotein)

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CYTOPLASM ORGANELLES

• Endoplasmic reticulum
• rough endoplasmic reticulum
• protein synthesis for exported proteins
• smooth endoplasmic reticulum
• no ribosomes , synthesis of carbohydrate of
  glycoproteins

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CYTOPLASM ORGANELLES, cont.

• ribosomes
• site of synthesis of proteins
• some exist attached to RER
• some ribosomes synthesize proteins used by the
  cell which makes the protein ( non export)
• NOTE RIBOSOMES ARE ESSENTIAL FOR ALL PROTEIN
  SYNTHESIS

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CYTOPLASM ORGANELLES, cont.

• Golgi apparatus
• membranous stack plus vesicles
• package and post process products from the
  endoplasmic reticulum

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Synthesis of exported proteins

• 1. Protein synthesis starts in the rough
  endoplasmic reticulum (RER)
• 2. The protein makes it way to the smooth
  endoplasmic reticulum (SER)
• 3. Next the protein is transported to the Golgi
  apparatus where it is packaged for export
• 4. Secretory vesicles pinch of the the Golgi and
  migrate to the plasma membrane
• 5. Fusion- vesicle fuses with the plasma membrane
  and releases protein(s) to the extracellular
  space ( secretion occurs)

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CYTOPLASM ORGANELLES, cont.

• Lysosomes
• membrane bound sac contains hydrolytic enzymes
• digest old organelles
• digest pathogens ( bacteria, fungi, viruses)

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CYTOPLASM ORGANELLES

• Peroxisomes
• membrane bound sac contains peroxidase and
  catalase
• important in metabolic reactions involving
  hydrogen peroxide
• used to detoxify harmful chemicals

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CYTOPLASM ORGANELLES, cont.

• Mitochondria
• oval shaped, double membranes and cross
  membranes called cristae
• site of synthesis of ATP used for energy in the
  cell

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CYTOPLASM ORGANELLES, cont.

• cytoskeleton
• microtubules
• hollow , 25nm largest
• also found in centrioles, flagella
• intermediate filaments
• 3 strands- 10 nm
• attaches to ribosomes, mitochondrion and other
  organelles

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CYTOPLASM ORGANELLES, cont.

• cytoskeleton
• microfilaments
• smallest- 7 nm
• used in mitosis also

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CYTOPLASM ORGANELLES, cont.

• centrosome
• a pair of centrioles
• plays a role in cell division
• composed of microtubules

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CELL EXTENSIONS

• microvilli ( brush border)
• increases surface area
• found on epithelial cells
• cilia
• hair like structures
• found in respiratory tract epithelial
• flagella
• tail like structure found on sperm

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cell connections

• desmosomes
• spot weld type ( intermediate filaments
• gap junction channels
• tight junctions -plastic collar

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TRANSPORT PROCESSES or how things get into and
out of cells

• simple diffusion
• passive
• movement of solute
• From higher solute concentration to lower

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TRANSPORT PROCESSES, cont.

• dialysis
• passive
• peritoneal dialysis

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TRANSPORT PROCESSES, cont.

• facilitated diffusion
• passive
• membrane protein carrier
• example- transport of glucose into cells

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TRANSPORT PROCESSES, cont.

• osmosis
• diffusion of WATER through a selectively
  permeable membrane
• movement of water is from higher to lower

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More on osmosis

• if red blood cells are put into WATER they will
  swell and burst.
• The water is HYPOTONIC in relationship to the
  internal environment of the RBC.
• Water moves into the cell

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More on osmosis

• if red blood cells are put into 2.5 NaCl, the
  cells will shrink.
• Water leaves the cell.
• The solution is HYPERTONIC

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More on osmosis

• if red blood cells are put into a solution of
  0.9 NaCl, they will stay the same size.
• Amount of water going into and out of the cell is
  equal.
• This solution (0.9 NaCl) is ISOTONIC.

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TRANSPORT PROCESSES, cont.

• active transport
• uses ATP
• from low to high possible
• muscle- pumps calcium ions, Na/K pump

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ENDOCYTOSIS( vesicles formed)

• phagocytosis
• active
• cell eating- intake of bacteria
• pinocytosis
• active
• cell drinking- intake of fluid and dissolved
  solutes

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ENDOCYTOSIS , cont.

• membrane mediated endocytosis.
• intake of specific molecules
• membrane receptors bind with specfic molecules
• example- uptake of hormones into target cells

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EXOCYTOSIS

• excretion- waste products put out of cell
• vesicle fuses with plasma membrane and releases
  waste to outside
• secretion- product put out of cell
• same as above, except product released is used

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CELL CYCLE

• INTERPHASE
• growth 1 G1
• synthesis- DNA replication takes place
• growth 2

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MITOSIS

• I. prophase-
• nuclear membrane disappears
• chromosomes supper coil
• II. metaphase
• double stranded chromosomes migrate to the
  equatorial plane

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MITOSIS, cont.

• III. anaphase-
• single stranded chromosomes form
• and migrate towards poles

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MITOSIS, cont.

• IV. telophase
• cytokinesis occurs
• nuclear membrane reforms

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MEIOSIS

• meiosis I and meiosis II
• synthesis of sperm and ovum

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Cell activities

• DNA REPLICATION
• the doubling of genetic material ( single
  stranded chromosome to double stranded chromosome
• TRANSCRIPTION
• synthesis of mRNA
• TRANSLATION
• synthesis of protein molecule

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Diseases and cells

• Cell growth and reproduction problems
• Atrophy- decrease cell size
• Hypertrophy- increase in cell size
• Hyperplasia- increase cell numbers ( nor normal)
• Neoplasm- new growth either benign or malignant
  (cancer)

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Cellular disease

• Cystic fibrosis- Cl- transport affected
• Duchenne muscular dystrophy- Ca ion in muscle
  cells affected
• NIDDM- membrane receptors for insulin are
  reduced
• Disorders that affect protein synthesis
• Sickle cell anemia