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 protein- digesting 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

• 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 cisternaecis, 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

LysosomesThe cell’s “stomach” – vesicles that contain digestive enzymes.

Primary lysosomes contain inactive enzymeswork 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 Peroxide- H2O2

– Free radicals

MitochondriaMitochondrion – 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

• Nuclear division (mitosis or meiosis)

• Cytoplasmic division – cytokinesis

• Mitosis is somatic (body) cell division

• Meiosis is reproductive cell division

MitosisHomologous 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