Transcript Cell structure part B

The Cellular Level of
Organization –Part B
Cytoplasm
• Cytosol
– Semifluid, mostly water
– Protein, carbohydrates, lipids, and inorganic
substances (ions)
– Many important metabolic reactions take
place here
– Cytoplasm is the cytosol plus the organelles
Organelles
“little organs” – have characteristic
appearance and have specialized functions in
cell growth, maintenance, repair and control.
Number and types of organelle vary with cell.
Two basic types:
nonmembranous
membranous
Ribosomes
• Made of ribosomal RNA and protein
– Free and associated with the endoplasmic
reticulum ( fixed ribosomes)
– Site of protein synthesis
– Nonmembranous, Temporary structures
made of large and small subunits
Proteasomes
• Hollow cylinders which contain proteindigesting enzymes ( proteases)
• Remove and recycle damaged or
denatured proteins
• Also play a role in the immune response
Endoplasmic reticulum (ER)
Endo – within Plasm – cytoplasm
Reticulum - network
Can be rough or smooth
Rough ER has ribosomes, makes proteins
for export outside of cell
Smooth Endoplasmic Reticulum
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Synthesis of phospholipids and cholesterol
Synthesis of steroid hormones
Synthesis and storage of triglycerides
Synthesis and storage of glycogen
Storage of ions ( e.g. Ca++ in muscle)
Detoxification and inactivation of drugs
Gogli apparatus (body, complex)
Made of flattened sacs called cisternae
cis, medial, trans
-Process, sort and deliver proteins and
lipids to the plasma membrane
-forms vesicles and lysosomes.
-forms new plasma membrane
The “UPS” of the cell
Vesicles
• Membrane bound sacs
• Formed during endocytosis or by golgi
apparatus
• Transport
• Renew membrane – membrane flow
Lysosomes
The cell’s “stomach” – vesicles that contain
digestive enzymes.
Primary lysosomes contain inactive enzymes
work at low pH
Found in large numbers in white blood cells
Intracellular digestion ( phagocytosis etc.)
worn-out organelles ( autophagy)
digestion of cell contents (autolysis)
Tay-Sachs disease
Peroxisomes
• Smaller than lysosomes
• Enzymes use molecular oxygen to oxidize
substances
• Reactions produce Hydrogen PeroxideH2O2
– Free radicals
Mitochondria
Mitochondrion – singular
Two membranes – inner folds called cristae.
Main function is the use of oxygen to produce
ATP – cellular (aerobic) respiration
These are the “power plants” of the cell.
Have their own DNA and RNA
Centrosomes and Centrioles
Centrioles are 2 cylinders of tubules arranged
at right angles.
9 + 0 array
Form the microtubules of the mitotic spindle
during cell division, and also make up a part of
cilia and flagella
Heart of the cytoskeleton
Flagella and cilia
• Cilia – “eyelashes” cilium
• 9+2 array
• Anchored to basal body
Flagella
Cytoskeleton
Microfilaments, intermediate filaments and
microtubules
Give the cell shape, and allow it to move – the
Musculoskeletal system of the cell.
Myofilaments are made of the protein actin
Myotubules are made of the protein tubulin
Inclusions
Usually contain chemical substances
produced by the cell, these are temporary
structures that are not surrounded by a
membrane.
Melanin, glycogen, triglycerides
ribosomes
Nucleus
• Double membrane called the nuclear
envelope
• Nucleoplasm
• Chromatin granules – unwound DNA
• Nucleoli – puts RNA and protein together
to make ribosomes
• Nucleus is essential for cell survival
The Cell Cycle
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Nuclear division (mitosis or meiosis)
Cytoplasmic division – cytokinesis
Mitosis is somatic (body) cell division
Meiosis is reproductive cell division
Mitosis
Homologous chromosomes
Cell cycle – from one cell division to the next
Interphase – “resting phase”
G1 – Gap1 – growth phase
S – Synthesis – replication of DNA
G2 – Gap 2
Nuclear division – mitosis or
karyokinesis
Prophase
Metaphase
Anaphase
Telophase
PMAT
Cytokinesis
• Contractile ring of actin microfilament
• Cleavage furrow
• Two new daughter cells
GPCR
GPCR
Steroid receptors
Control of cell division
• How many times a cell divides depends on
the type of cell
• Stem cells retain the ability to divide and
differentiate
• Cell senescence
• Telomeres
• Levels of proteins called kinases and
cyclins
Control – contd.
• Cell size
• External factors –hormones and growth
factors
• Contact inhibition
Loss of control over division
• Neoplasm or tumor
• Benign tumors remain in a single location
• Malignant tumors (cancer) can spread or
metastasize
• Oncogenes – want these turned “off”
• Tumor suppressor genes – want these
turned “on”
• Apoptosis