CYTOLOGY
THE STUDY OF CELLS FUNCTION
CELLULAR ACTIVITIES
Transport systems – Processes of
Transport Across Cell Membrane
The Cell Cycle – Cellular Activities
from Formation to Death or Division
Protein Synthesis – using DNA &
RNA to make proteins
TRANSPORT SYSTEMS
Passive Transport (does not require
energy)
Active transport (does require
energy; ATP most common form)
PASSIVE TRANSPORT
SYSTEMS
Diffusion
Facilitated diffusion
Osmosis
PASSIVE TRANSPORT
SYSTEMS: DIFFUSION
Molecules in constant motion
 Molecules move from [high]
to [low]
Continues until Equilibrium
DIFFUSION
Diffusion through a membrane
FACILITATED TRANSPORT OR
DIFFUSION
Requires special proteins (enzymes)
Integral Membrane Proteins
“Escort” molecules across membranes (e.g.
Glucose)
Facilitated Diffusion
OSMOSIS
“Special case” of diffusion
Only water moves
Water moves across a selectively
permeable membrane
Water moves from [low solute] to [high
solute]
OSMOSIS
Tonicity
Concentration of solutes in a solution
(relative to the concentration inside the
cell)
Isotonic = concentration is the same
Hypotonic = lower concentration of
solutes
Hypertonic = higher concentration of
solutes
TONICITY
ACTIVE TRANSPORT
SYSTEMS
Facilitated active transport
Endocytosis
Exocytosis
FACILITATED ACTIVE
TRANSPORT
Molecules are moved against a
concentration gradient
Integral Proteins act as Carrier Molecules
Sodium and potassium pump moves Na+
out of cell and K+ into cell
ENDOCYTOSIS
Materials accumulate at surface of plasma
membrane
Membrane evaginates or invaginates,
pinches off
Includes:
- phagocytosis – engulfment of large solids
(e.g. WBCs & bacteria/viruses)
- pinocytosis – engulfment of extracellular
fluid
EXOCYTOSIS
Releases substances outside cell
Secretory vesicles fuse to cell membrane
Cellular products, e.g., secretion
Cellular wastes
Endocytosis
Exocytosis
CELL CYCLE
Interphase
Cell Division
- Mitosis
- Cytokinesis
CELL CYCLE:
INTERPHASE
* High metabolic activity
* Protein synthesis
* DNA replication (46 
92)
CELL CYCLE: MITOSIS
Growth & Repair
4 phases:
-
Prophase
Metaphase
Anaphase
Telophase
MITOSIS: PROPHASE
Chromatin condenses
into chromosomes
Centrioles organize
spindle
Spindle fibers attach to
centromeres
Nuclear membrane
disassembles
Nucleolus disassembles
MITOSIS: METAPHASE
Spindle aligns
chromosomes
Alignment is around
“equator”
Alignment is random
MITOSIS: ANAPHASE
“Daughter” chromosomes
separate
Chromosomes are moved
toward poles
Cytoplasm elongates &
cytokinesis begins
MITOSIS: TELOPHASE
“Reverse” of prophase
Chromosomes relax into
chromatin
Nuclear membrane
reassembles
Nucleolus reassembles
CELL CYCLE:
CYTOKINESIS
* Division of the cytoplasm and organelles
* Begins during anaphase
* Completed following telophase
Mitosis
CYTOLOGY
PROTEIN SYNTHESIS
PROTEIN SYNTHESIS
Involves DNA & RNA
DNA codes for proteins
RNA assembles proteins
Gene = a segment of DNA that codes for
one protein
The sequence of bases (nucleotides) carries
the information
Protein Synthesis cont.
T, A, C, G in DNA
U, A, C, G in RNA
A single gene has between 300 – 3000 base
pairs
In DNA, each 3-base sequence (triplet)
specifies one amino acid
PROTEIN SYNTHESIS
Each strand of DNA is complementary to
the other
Messenger RNA is complementary to DNA
& carries instructions from DNA to
ribosomes
Protein synthesis occurs at ribosomes
RIBONUCLEIC ACID (RNA)
 Messenger RNA (mRNA)
- polynucleotide strand that is
complementary to DNA
- carries instructions from DNA to ribosomes
 Transfer RNA (tRNA) – transports amino acids
to ribosomes
 Ribosomal RNA (rRNA) – part of ribosomes
The preview Image has been scaled down to fit the screen. Actual image is both larger and clearer.
DNA Replication
PHASES OF PROTEIN
SYNTHESIS
Transcription
- Complementary mRNA is made from a DNA
gene (sequence coding for a protein)
Translation
- mRNA’s information is used to assemble
proteins with the help of tRNA & rRNA
Overview of Protein Synthesis