Week Three Chapter 5 Cell structure and function
Cell Theory (the study of cells is cytology)
All organisms are composed of one or more cells.
The cell is the basic living unit of organization for all living things
All cells arise from preexisting cells
Cells contain all of the hereditary information
3 basic structures of all cell types:
1. plasma membrane - a physical boundary that separates
the cell from the outside environment
2. organelles- internal structures that are suspended I the
cytoplasm
3. cytoplasm – sort of jelly-like substance, mostly water.
Prokaryotes v. eukaryotes
Prokaryotes: the term means “before the nucleus”, they lack a distinct nucleus,
though some have a nuclear area where DNA is found they lack a membrane to
contain the DNA. Smaller than eukaryotes, grow faster. Bacteria and
cyanobacteria, all are members of the kingdom Prokaryotae or Moneran
Characteristics: lack most membrane bound organelles, have DNA in a
concentrated region, tend to grow rapidly and divide often.
Eukaryotes: protists, fungus, plants and animals. Characteristics: possess
specialized membrane-bound organelles, Nuclear membrane, other specialized
membranes
Cell Size:
Prokaryotes .2 –5 micrometers, eukaryotes 10-100 micrometers
Surface to volume ratio limits cell size (OVERHEAD)
Volume increases with the cube of the diameter (V=d3)
Surface area increases with the square of the diameter
As a cell grows its volume (cytoplasm) increases at a faster rate
than its surface area (plasma membrane)
Cell Shape
Related to function – epithial cells are plate like, roughly square or
spherical, nerve or muscle cells are elongated
Micrsoscope invented in the 1600’s
Cell Structure: Eukaryotes see drawing on page 89, figure 5-8)
Cytoplasm: material outside of nucleus, consists of fluid and particles and
membranes
Nucleoplasm: material inside nucleus
Nucleus – largest organelle)
 Nuclear envelope
 Double Membrane
 Has many nuclear pores
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Nucleolus (nuceioli plural)
 Site of ribosome assembly
 Ribosomes leave through pores and are found free in the cytoplasm or
associated with Endoplasmic reticulum
Ribosomes are organelles that are part of the protien synthesis machinery
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Genetic Material: DNA
 Chromatin
 Seen in cells that are not dividing
 Decondensed DNA associated with RNA and proteins
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Chromosomes
 Seen in cells that are dividing
 Condensed DNA in a highly organized and compact form
Endoplasmic reticulum
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sets of membranes continuous with the nuclear and plasma
membranes
Membranes act to divide up the cytoplasm into compartments
and channels
Two types:
1. rough ER: have ribosomes, mat be free or attached to
the rough ER, ribosomal function: development of the
primary structure of proteins
2. smooth ER: lack ribosomes, function: phosolipid, steroid
synthesis
Golgi Complex)
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stacks of flattened membranes (look like a stack of pita bread)
sets of smooth membranes derived from the ER
Functions: sorting and modifying proteins, ultimately transports
products to the plasma membrane or are stored in the
cytoplasm, also produces the lysosomes
Lyosomes (in animals)
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Contain powerful digestive enzymes
Function as the cell’s recycling center by digesting worn-out
organelles or materials ingested by cell
Rheumatoid arthritis is due to damage in joints due to leaky
white blood cell lysosomes
Microbodies
Various organelles which regulate different metabolic reactions such as
peroxisomes break down hydrogen peroxide, glyoxysomes are important in
germiniating seeds
Organelles involved with Energy Production and Utilization
Mitochondria
 The power plants of the cell
 Site of cellular respiration, which converts organic
molecules to ATP
 Double membrane bound; specialized membranes for
energy production
 Have a small amount of their own molecules of DNA,
ribosomes
Chloroplasts
 Site of photosynthesis
 Also double membrane bound
 Inner structure
 Stacked membrane system (thylakoids) (3rd system of
membranes)
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Pigments:chorophyl and others
Also have their own DNA molecules
Other plastids include leukoplasts which store starch and are colorless,
and chromoplasts which store colored pigments
READY FOR THE EXAM?