Download ANPS 019 Beneyto-Santonja 09-10

ANPS 019 09/10/12 Beneyto
Transcription: making a copy of one strand of the DNA into RNA (think transcribe)
Translation: converting a nucleotide sequence into an amino acid sequence (think translate)
There are 3 kinds of RNA involved in the process
 Ribosomal RNA (rRNA): Combined with proteins to make ribosomes
 Messenger RNA (mRNA): the message strand that carries the code for a protein from the
DNA into the cytoplasm
 Transfer RNA (tRNA): Cytoplasmic RNA strand folded into cloverleaf; Binds an amino
acid at one end
Where does translation happen?
 Translation always begins on free ribosomes in the cytoplasm.
 Proteins destined for the cytoplasm (ie-cytoplasmic enzmes) or the nucleus (ie-histone)
are usually synthesized entirely on the free ribosome within the cytoplasm.
 After translation, these new proteins are simple released by the ribosome into the
cytoplasm.
 The cytoskeleton will direct these proteins to their destination in the cytoplasm or to the
nucleus.
 Some proteins may not be ‘safe’ floating in the cytoplasm.
 Others may need to be inserted in a phospholipid bilayer or packaged within membrane
vesicles so they can be released from the cell by exocytosis.
 These are membrane associated proteins
o There is information contained in its coding that tells the free ribosome to move
the growing protein into the endoplasmic reticulum. There, the protein will be
associated with membrane as it forms.
The fat of new proteins
 Proteins associated with membranes are produced in rough ER, then sent to the Golgi
apparatus where they are modified, packaged, and directed to their final destination
 Three types of Proteins are processed through the ER/Golgi:
o Lysosomal Proteins (enzymes)
o Proteins destined for exocytosis from secretory vesicles
o Integral and Peripheral membrane proteins
Different mechanisms of cell-cell communication we will study in this course
 Direct Communication  through gap junctions
 Paracrine Communication  through extracellular fluid
 Endocrine Communication  through the circulatory system
 Synaptic Communication  across synaptic clefts
Cell Communication
 Most messages influence the activity of the target cell
o Activation of enzyme systems
o Stimulation of secretion from cell
o Opening of ion channels in plasma membrane (electrical activity)
o Stimulation of cell division
o Activating/inactivating of genes (increasing or decreasing protein synthesis)
Tissues
 Tissues are collections of specialized cells and cell products organized to perform a
limited number of functions
o Histology = study of tissues
 All cells in the body are classified into one of the four tissue types

o Epithelial (Epithelium and Glands)
o Connective
o Muscular
o Nervous
Epithelial Tissue; text readings: Chapter 4 pp. 109-120
o Types of Epithelial Tissue
 Epithelial sheets (“epithelium”)
 A layer of tightly adjoining related cells
 Locations:
o Body surface (outermost part of skin)
o Lines all hollow structures in body
 Functions:
o Physical Protection
o Control Permeability
o Produce specialized secrections
 Glands
o Key Characteristics of Epithelial sheets:
 Cells are polarized
 Little space between cells
 Cells tightly held together by junctions
 Avascular (no blood vessels between cells)
 Specialized for absorption or protection
 Continuous rate of cell division
o Epithelial Cells have Polarity (sided-ness)
 Apical (free or exposed surface)
 Lateral (neighboring epithelial cells)
 Basal (surface anchored to connective tissue)
o Epithelial cells are attached at the basal surface to a basement membrane
 The epithelial cells are attached to connective tissue through the glue-like
proteins of the basement membrane
 We often use the phrases “basal lamina” and “basement membrane”
interchangeably.
o The avascular concept
 Little space between adjacent cells for blood vessels
 Epithelial cells are usually helpt alive by diffusion of oxygen and
nutrients from the blood vessels in the adjacent connective tissue below
the basal lamina
 Epithelial layers are limited in thickness – diffusion is poor over long
distances or dense areas
o Some Epithelial Cells may have specializations on their apical surfaces
 Microvilli: small fingerlike projections of the apical or basal surface of
an epithelial cell (may be hundreds per cell)
 Microvilli increase surface area for the cell
 Cilia: long slender extensions of the apical cell surface
 Have a core of microtubules
 Cilia have rhythmical movement
o Epithelial Cells are tightly held to their neighboring epithelial cells
 Cells attached via cell adhesion molecules
 Cells attach at specialized cell junctions
 Gap junctions
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Desmosomes
Tight junctions
Lateral interdigitations