Transcript CH 3 Part 2 - Catherine Huff`s Site

The Amazing Cell, Part 2
Cytoplasm
• The inner substance of the cell, excluding the
nucleus.
• Components include:
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Cytosol
Cytoskeleton
Organelles
Inclusions
Cytosol
• The fluid of the cell
• Viscous (thick, sticky consistency),
• Semi-transparent liquid composed of
dissolved electrolytes, amino acids,
and simple sugars.
• Proteins suspended within fluid give
fluid its thick, jellylike consistency.
• Proteins within the cytosol are
enzymes that are important in
metabolic activities of the cell.
Cytoskeleton
• Three dimensional frame/structure for the cells
• It is neither rigid or permanent.
• Flexible and fibrous; changes in accordance to activities of the cell.
• Gives support and shape to the cell, enables cell to move and
provides direction for metabolic activity.
• Also anchors organelles
• These fibers are not enclosed in a membrane
• Types of fibers that comprise cytoskeleton:
• Microtubules
• Intermediate fibers
• Microfilaments
Microtubules
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Thickest fibers, protein, and are long and hollow
Grow out from the cell center, near nucleus
Form cables that organelles attach too.
Proteins move these organelles along microtubules
throughout cell, like a railroad track for the organelles
• Can be easily disassembled and re-asembled to form new
paths or take on new direction
• Composed of a pair of spherical molecules -tubulins, which
are linked together in a spiral chain
Intermediate Fibers
• Woven, ropelike fibers that possess high tensile strength
• Are able to resist pulling forces on the cell by acting as
internal guy wires
• Toughest and most permanent part of the cytoskeleton
• Composed of proteins - variable depending on cell
function
• May take on different names:
• Tonofilaments-in epithelial cells, mostly keratin
• Neurofilaments- in nerve cells
Microfilaments
•Located near cell surface on the cytoplasmic side of the
plasma membrane.
•Are arranged in bundles and meshworks.
•Provide tensional support like cables on a bridge
•Composed of the contracticle protein actin and the motor
protein myosin
•Play key role in cell’s ability to change shape, break apart
during cell division and form outpouchings and involutions.
•Are assembled where and when needed.
•Cell’s activity determines how many and where
microfilaments are position
Organelles
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“little organs”
• Membrane bound structures within cytoplasm that have specialized
functions.
• Is separated from cytoplasm it’s own membrane so can maintain own
internal environment.
• Do not have glycocaylx coating
• Compartmentalization is good for metabolic processes such as food
absorption, energy production, and excretion.
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Mitochondria
Ribosomes
Golgi Apparatus
Endoplasmic Reticulum
Lysosomes
Peroxisomes
Mitochondria POWERHOUSE
• One of largest organelles
• Called “powerhouse of the cell” because produces up to 95% of
energy that fuels the cell.
• Nutrient molecules (i.e. glucose) are broken down to produce
intracellular fuel.
• Location of many biochemical reactions.
• Amino acid and fat catabolism
• Where respiration takes place
• Oxygen consumed
• Carbon Dioxide released
Mitochondria
• Active cells have higher energy demands so have more
mitochondria.
• Heart cells
• Mitochondria can divide through fission-or the
pinching themselves in half.
• Tend to be located at portion of cell where energy
requirements are the greatest.
• Contain DNA, RNA and enzymes.
• DNA and RNA are similar to those found in bacteria
• Provide selves with 13 proteins while nucleus provides
the remaining 50.
Where are the
Mitochondria
Mitochondrial shape
• Tend to be elliptical and round
• Outer smooth membrane
• Inner involuted membrane.
• Inner membrane forms cristae which
increase internal working area and
matrix (enzyme-rich liquid housed in
mitochondria).
• Cristae are site of ATP production
• Active mitochondria possess more
cristae than inactive ones.
Ribosomes
• Most common organelle in the cell.
• Made of two globular subunits that fit together.
• Composed of protein and rRNA.
• Small, but important in the synthesis of proteins for intracellular use.
• Can attach and detach from membranes and move freely within the cell.
• Move back and forth between endoplasmic reticulum and cytoskeleton depending
on type of protein they are making.
Endoplasmic Reticulum
Endoplasmic Reticulum (ER) - Factory
• Series of flattened membranes stacked on one another and bent into crescent
shape.
• Composed of single lipid bi-layer
• Continuous with the membranes of the nucleus and golgi apparatus
• May be rough or smooth depending on if it contains ribosomes or not.
• Rough ER is involved in production of protein assembled by ribosomes
• New Proteins are moved inside ER into passageways.
• Cisternae -Location of protein modification before being moved to Golgi.
• Smooth ER is connected to Rough ER and is active in synthesis and storage
of lipids (phospholipids and steroids)
• In liver may also break down drugs and break down glycogen into
glucose => detoxification
• Proportion of smooth to rough ER varies depending on the cell’s synthetic
activities.
Golgi Apparatus – Shipping!
• Found near nucleus and is similar in structure to ER
(composed of cisternae)
• Receives proteins produced by ER via transfer sacs.
• Proteins are modified (add carbohydrates) here as they
move from fold to fold.
• Once completed they are packaged into vesicles and travel
out into other parts of the cell or to cell membrane.
• Act as the modification, packaging and distribution center.
• Also functions to synthesize polysaccharides.
Lysosomes
• Specialized vesicle formed by Golgi apparatus.
• Contains hydrolytic or digestive enzymes
• Lysosome fuses with other vesicles and digests them.
• Principal responsibility to breakdown nutrient molecules and digestion of
cellular debris.
• Considered “stomach of the cell”.
• When cells die, lysosomes are triggered to burst, release digestive enzymes and
digest other portions of the cell.
• This is called autolysis.
• May also release enzymes outside of cell to assist with breakdown of
extracellular material.
• Increase in numbers as cell ages.
Lysosome Action
1. Material from outside is
drawn into a forming
vesicle.
2. Plasma membrane
pinches off vesicle
3. Vesicle transports
material into cell
4. Lysosome approaches
5. Lysosome fuses with
vesicle and inserts its
digestive enzymes
6. Contents of vesicle are
digested and
transported to other
regions of the cell.
Peroxisomes
• Membranous sacs containing enzymes found throughout
the cell.
• Reproduce through pinching in half.
• Common in liver and Kidney cells
• Important in detoxification of various molecules.
• Remove free radicals- normal products of cellular
metabolism but can be harmful in large numbers
• Carry two major enzymes:
• Peroxidases-assist in conversion in free radicals to
hydrogen peroxide.
• Catalases-reduce hydrogen peroxide to water.
Inclusions
• Packaged units of metabolic products or
substances that the cell has engulfed.
• May or may not be membrane-bound.
• Vacuoles are larger than vesicles but are of
similar structure.
Centrioles
• Small, hollow-like cylinders composed of
microtubules.
• Found in pairs perpendicular to one another.
• Visible during cell division near nuclear envelope
• Help to organize spindle fibers during cell division.
• May also form bases of cilia and flagella (basal
bodies).
Nucleus
• Largest organelle in the cell.
• Control center or “brain” of the cell.
• Primary functions are to maintain hereditary
information of the species and to control cellular
activities through protein synthesis.
• Some cells may be multi-nucleated while some are
anucleated.
• What is this and where is it found?
• What is a disadvantage to no nucleus?
Nuclear Anatomy
• Divided into four parts:
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Nuclear Envelope or membrane
Nucleoplasm
Chromatin
Nucleoli
Nuclear Envelope and
Nucleoplasm
• Separated from cytosol by a
nuclear envelope composed of
two lipid bilayers
• Outer layer is continuous with
Rough ER.
• Contains nuclear poreschannel through entire
thickness.
• Allow transport of protein and
RNA.
• Area between bilayers is space
called perinuclear space.
Nucleoplasm
• The gel-like substance that fills the nucleus.
• Resembles cytosol.
DNA, RNA and Chromatin
• DNA and RNA are composed of nucleotides.
• What are they?
• How do they pair?
• What does DNA form?
• Chromatin-fibers made up of DNA and globular
proteins called histones
• Nucleosome- single strand of DNA wound around
8 histone molecules.
• During cell divison, chromatin condenses into
super-coiled, x-shaped structure called
chromosomes.
Nucleoli
• Not membrane bound
• Where ribosomal subunits are made
• Contain DNA that governs synthesis of rRNA.