Lecture 1 The Cell Flashcards
The Cell
THE CELL
• Cells interact with extracellular environment through active processes (active transport - cell uses energy to do this).
1) Exocytosis: expulsion of materials out of the cell by fusing of a vesicle membrane with the cell membrane
2) Endocytosis: uptake of materials into the cell
THE CELL
Endocytosis:
2 types
a) Pinocytosis: “cell drinking”
b) Phagocytosis:
“cell eating”
Structure of cell
CELL MEMBRANE
•
aka plasma membrane
• Surrounds the cell
Composed of a phospholipid bilayer and proteins:
- phospholipids: act as diffusion regulators.
- proteins: structural reinforcements and receptors for certain hormones, neurotransmitters and immunoglobulins (antibodies).
• Semipermeable:
- provides a selective barrier that regulates transport of substances into and out of the cell.
CYTOPLASM
• aka cytosol
• Clear liquid enclosed in the cell by the cell’s membrane.
• Includes organelles and inclusions and also spaces or cavities called vacuoles.
• Provides a medium (fluid)
in which other
organelle’s function.
ORGANELLES
• Organelles are metabolically active specialized structures within the cell.
• Organelles allow each cell to function according to its genetic code.
• Major organelles are:
• Nucleus
• Mitochondria (sing: mitochondrion)
• Ribosomes
• Endoplasmic reticulum
• Golgi Apparatus
• Lysosomes
• Cytoskeleton
NUCLEUS
•
Plural - nuclei
Largest, densest organelle
Usually single nucleus present but cells can be:
- Binucleated:
- cardiac muscle cells
- parenchymal liver cells
- Multinucleated:
- osteoclasts
- skeletal muscle cells
• Production of:
- 1) DNA (deoxyribonucleic acid):
cell’s genetic information
- 2) RNA (ribonucleic acid):
carries info from the DNA to sites of actual protein synthesis in the cytoplasm.
Present in all cells except mature red blood cells and blood platelets.
COMPONENTS of a NUCLEUS
• NUCLEOLUS:
-contained in the nucleus
-produces rRNA and nucleotides of two other types of RNA
• CHROMATIN (form of DNA):
-contains chromosomes
-looks like diffuse stippling when the cell is viewed at lower-power microscopically
• NUCLEOPLASM:
-fluid portion that contains important proteins
NUCLEAR ENVELOPE:
-a double layered membrane
ENDOPLASMIC RETICULUM
• The ER consists of parallel membrane-bound channels.
• All membranes are interconnected.
• Connected to cell membrane, the nuclear membrane and some organelles (“highway system for the cell”).
• Primary function: modification, storage, segregation and transport of proteins that the cell manufactures.
• Can be classified as rough or smooth.
ROUGH ENDOPLASMIC RETICULUM
• Contains ribosomes on its outer surface
• Ribosomes - particles composed of protein and
RNA which synthesize protein (“protein factories”)
The protein molecule can then be transported to Golgi Apparatus for further processing
SMOOTH ENDOPLASMIC RETICULUM
• No ribosomes
• Contains enzymes involved in
manufacturing various lipid molecules and steroid hormones.
Golgi Apparatus
• “Chemical processing and packaging center”
• Second largest organelle
• A stack of 3 to 20 flattened membranous sacs (looks like a stack of pancakes).
• Function: sorts, condenses, packages and delivers proteins from the RER.
• Processes the protein molecule created by the ribosomes.
• Attached to the cell’s membrane and release its contents by exocytosis.
MITOCHONDRIA
• “Powerhouse” of the cell.
- Composed of two membranes: (the inner membrane is folded to increase in surface area forming cristae)
• Most numerous organelle in the cell
• Releases energy from food molecules and transform energy into ATP (adenosine triphosphate).
LYSOSOME
• “Sewer system” of the cell (destroys worn cell parts).
• Membranous sacks produced by the Golgi
Apparatus.
• Contains hydrolytic (hyaluronidase) and digestive enzymes capable of digesting substances that enter cells.
CYTOSKELETON
The components include:
-microfilaments
-intermediate filaments
-microtubules.
• Components give basic stability to the cell as a whole, functioning like reinforced girders.
• The cytoskeleton also compartmentalizes (sorts out) the cytoplasm, creating preferred
“freeways” for the movement of molecules formed by cellular processes.
Cytoskeleton
3 Compnents
• The components include:
-microfilaments
- intermediate filaments
- microtubules.
MICROFILAMENTS:
• Delicate, threadlike, microscopic structures of specialized protein, arranged in meshwork of bundles.
• Cause various kinds of cellular movements (such as in muscle cells as myofibrils).
• Responsible for cell motility.
Microtubules
MICROTUBULES:
• Long slender tubes with diameters 2 or 3 times greater than microfilaments.
• Usually stiff, forming an
interna skeleton within a cell which helps maintain the shape of the cell.
Provides strength to the structure of:
- cilia (shorter, many)
- flagella (longer, few)
centrioles mitotic spindle
CYTOSKELETON
INTERMEDIATE FILAMENTS:
INTERMEDIATE FILAMENTS:
•Various types of thicker, threadlike microscopic structures within the cell.
• Ex: tonofilament - important in intercellular junctions.
INCLUSIONS
INCLUSIONS
• Metabolically inert substances that are transient over time in the cell.
• Consist of cellular products that remain in a cell only temporarily.
• Ex: nutrients such as glycogen, lipids and the pigment melanin.
INTERCELLULAR JUNCTIONS*
INTERCELLULAR JUNCTIONS
Tight Junctions
TIGHT JUNCTONS:
• Closes intercellular space between cells by fusing cell membranes together.
• Prevents the movement or loss of fluid.
• Location:
- cells that line inside of the small intestine
DESMOSOMES:
DESMOSOMES:
• Bind cells together by creating “spot weld between adjacent membranes.
• Location: cells of the outer skin and oral
Desmosomes
Desmosome - Tonofilament Complexes)
HEMIDESMOSOMES:
HEMIDESMOSOMES:
• Attachment of cell to an adjacent non-cellular surface.
• Smaller attachment plaque from the cell’s side (half of a desmosome).
• Used in attachment of epithelium to connective tissue
ex: basement membrane in oral mucosa).
• Allows gingival tissue to adhere to the tooth surface by epithelial attachment.
GAP JUNCTIONS:
GAP JUNCTIONS:
• Form tubular channels between cells that allow substances to be exchanged.
• Location:
- muscle cells of the heart.
- digestive tube.
Gap junctions
LIFE CYCLE OF A CELL
- Interphase (DNA replication)
- Mitosis (Cell Division)
- Cytokinesis (Cytoplasmic Division)
- Differentiation
Meiosis - occurs during the maturation of sex cells (will be discussed later).
INTERPHASE
• Stage in the life cycle when a cell grows and forms new organelles.
• Period of growth and activity between mitoses.
• Consists of 3 phases:
- G1 phase: the initial resting phase of cell growth.
- S phase: DNA replication (chromatin and centrosome replication)
- G2 phase: the second resting phase of cell growth.
• It terminates when the cell begins to undergo mitosis.
INTERPHASE
MITOSIS
MITOSIS
• Continuous process during which the nuclear parts of a cell are divided into two equal daughter cells.
• The stages of mitosis include:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
(Refer to table 7-2 in text Pg. 82)
Mitosis
1) Prophase
• Chromatin condenses into chromosomes.
• Replicated centrioles move to opposite poles.
• Nuclear membrane and nucleolus disappear.
1) PROPHASE
2) METAPHASE
• Chromosomes become arranged midway between the centrioles.
• Spindle fibers from the centrioles become attached to the centromeres of each chromosome.
2) METAPHASE
3) ANAPHASE
• Centromeres split and each chromosome separates into 2 chromatids.
• Chromatids migrate to opposite poles by the mitotic spindle.
• Spindle fibers shorten and pull individual chromosomes towards centrioles.
3) ANAPHASE
4) TELOPHASE
4) TELOPHASE
• Division into 2 daughter cells.
• Chromosomes elongate and form chromatin threads.
• Nuclear membranes appear around each chromosome set.
• Nucleoli appear.
• Microtubules disappear.
CYTOPLASMIC DIVISION
• aka Cytokinesis
• Process by which all cytoplasmic components of the cell are divided into two identical daughter cells following mitosis.
DIFFERENTIATION
• Cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type.
- Ex: ovum + sperm = fetus
This organelle’s primary function is modification, storage, segregation and transport of proteins that the cell manufactures.
Endoplasmic Reticulum
Exocytosis is uptake of materials into the cell, while endocytosis is expulsion of materials out of the cell.
B. Both statements are false.
What phase of mitosis is this?
Metaphase
These intercellular junctions form tubular channels between cells that allow substances to be exchanged.
GAP
