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Questions and Answers
What are the two main types of organelles found in the cytoplasm?
Which type of Endoplasmic Reticulum is characterized by the presence of ribosomes?
What is the main function of the Rough Endoplasmic Reticulum?
Which of the following organelles is not a membranous organelle?
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How does the Smooth Endoplasmic Reticulum differ from the Rough Endoplasmic Reticulum?
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What is a key structural feature of the Endoplasmic Reticulum?
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Which of the following is NOT a function of the Rough Endoplasmic Reticulum?
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What type of connection exists between two sacs of the Endoplasmic Reticulum?
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What is one of the main functions of the smooth endoplasmic reticulum (SER)?
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What are the two different-sized subunits of ribosomes primarily made of?
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Where are proteins synthesized that are intended for secretion or storage?
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What characterizes the Golgi Apparatus?
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What does the Golgi Apparatus NOT produce?
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What is the primary function of mitochondria?
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What is a structural feature of the inner mitochondrial membrane?
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Which of the following is NOT typically synthesized by the Golgi Apparatus?
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What is the function of lysosomal enzymes?
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How many molecules of ATP are produced under aerobic conditions from one molecule of glucose?
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What structure encloses the matrix space in mitochondria?
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Which organelles contain oxidases and catalase to regulate harmful substances?
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How are new mitochondria formed?
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What is the primary role of the cytoskeleton?
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What is formed when primary lysosomes fuse with other vacuoles?
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Which of the following correctly describes intermembrane space?
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What is the primary function of microtubules in addition to their role in the cytoskeleton?
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Which statement accurately describes the arrangement of microtubules in centrioles?
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What is the length range of cilia typically found on ciliated cells?
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What structural pattern is primarily observed in both cilia and flagella?
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What role do basal bodies play in relation to cilia and flagella?
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Study Notes
The Cytoplasm
- Cytoplasm is a part of protoplasm (the interior of a cell) not including the nucleus.
- Cytoplasm consists of a fluid matrix containing organelles and deposits of carbohydrates, lipids, and pigments.
- Cytoplasmic organelles can be membranous or non-membranous.
- Membranous organelles include: Endoplasmic Reticulum, Golgi bodies, Mitochondria, Lysosomes, and Peroxisomes (Microbodies).
- Non-membranous organelles include: Ribosomes, Cytoskeletal elements, and Centrioles.
Endoplasmic Reticulum (ER)
- ER is a network of membranous sacs that communicate with each other in a three-dimensional network, creating a continuous membrane.
- ER is composed of a "lipoprotein" membrane with two surfaces: one facing the cytoplasm and one facing the cavity of the flattened sac (cisternae).
- The ER membrane is about 5 nm thick and more stable and less fluid than the cell membrane.
- ER exists in three forms - lamellar, vesicular, and tubular - which can be converted into each other.
- Two types of ER:
- Rough Endoplasmic Reticulum (RER)
- Smooth Endoplasmic Reticulum (SER)
Rough Endoplasmic Reticulum (RER)
- RER has ribosomes on the cytoplasmic surfaces of its membranes, giving it a granular appearance.
- RER is prominent in cells specialized for protein secretion.
- RER consists mainly of lamellar forms interconnected by short tubular segments.
- The primary function of the RER is to separate proteins destined for export or intracellular use.
- Additional RER functions: initial glycosylation of glycoproteins, synthesis of phospholipids, assembly of multichain proteins, and certain posttranslational modifications of newly formed polypeptides.
Smooth Endoplasmic Reticulum (SER)
- SER lacks the ribosomes associated with RER, giving it a smooth appearance.
- SER cisternae are more tubular than RER cisternae and appear as interconnected channels of variable shape and sizes.
- SER has a variety of functions including:
- Metabolism of small molecules
- Synthesis of lipids and steroids
- Cellular detoxification
Ribosomes
- Ribosomes are small electron-dense cytoplasmic particles, about 20x30 nm in size.
- Ribosomes are composed of four types of ribosomal RNA (rRNA) and almost 80 ribosomal proteins.
- Each ribosome consists of two different-sized subunits formed within the nucleolus.
- Subunits leave the nucleus and participate in protein synthesis in the cytoplasm.
- Ribosomes play a crucial role in translating the message during protein synthesis.
Ribosome Occurrence
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Ribosomes occur as:
- Free polyribosomes
- Ribosomes attached to the membrane of RER.
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Proteins synthesized for use within the cell are synthesized on free polyribosomes, while proteins that can be secreted or stored in the cell are synthesized on RER ribosomes.
Golgi Apparatus (GA)
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GA is composed of three distinct smooth-membrane-limited compartments:
- Slightly curved stacks of 3-10 flattened cisternae
- Numerous small vesicles
- Few large vacuoles at one pole of the GA.
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GA completes posttranslational modifications, packages, and assigns an address to products synthesized by the cell.
Golgi Apparatus Function
- GA has a convex, forming face near the RER, and a concave, maturing face on the opposite side.
- Transitional vesicles from RER are transported to the forming face for further processing in GA.
- Vesicles detach from the maturing face as secretory granules.
Golgi Apparatus Products
- GA produces three kinds of products:
- Secretory granules
- Primary lysosomes
- Lipoprotein vesicles
Mitochondria
- Mitochondria are spherical or filamentous membranous organelles 0.5-1 m wide and up to 10 m length.
- These organelles transform the chemical energy of metabolites present in the cytoplasm into energy that is easily accessible to the cell.
- Mitochondria are chemically composed of protein, lipids, and small quantities of DNA & RNA.
Mitochondria Structure
- Mitochondria are structurally composed of an outer mitochondrial membrane and an inner mitochondrial membrane.
- The inner mitochondrial membrane projects folds, termed cristae, into the interior of the mitochondrion.
- The space located between the two membranes is called the intermembrane space, while the space enclosed by the inner membrane is called the intercristae, or matrix, space.
- The matrix is rich in protein and contains some DNA and RNA.
- The matrix also exhibits rounded electron-dense granules rich in cations and enzymes for the citric acid (Krebs) cycle and fatty acid -oxidation.
Mitochondria Energy Production
- Under aerobic conditions, the combined activity of extramitochondrial glycolysis, the Krebs cycle, and the electron transport system gives rise to 36 molecules of ATP per molecule of glucose. This is 18 times the energy obtainable under anaerobic conditions (glycolysis)
Mitochondria Division
- Mitochondria divide to form new mitochondria by accretion of material that leads to growth and subsequent cleavage (fission) of itself.
Lysosomes
- Lysosomes are membrane-limited vesicles, usually spherical, about 0.05-0.5 m in size.
- They contain over 40 types of hydrolytic enzymes whose main function is intracytoplasmic digestion.
- Lysosomal enzymes are synthesized and segregated in the RER then transferred to the GA, where the enzymes are modified and packaged as lysosomes.
Lysosome Formation and Function
- Lysosomes are formed as primary lysosomes (PL), then fuse with phagocytotic vacuoles or vacuoles of cytoplasmic debris to form secondary lysosomes (SL).
- SL are those in which digestion occurs.
- After digestion, metabolites diffuse to the cytoplasm, and undigestible compounds are retained within vacuoles. These vacuoles may discharge outside the cell or accumulate in the cytoplasm.
- Lysosomes are sites of intracellular digestion and turnover of cellular components.
Peroxisomes (Microbodies)
- Peroxisomes are spherical membrane-limited organelles, about 0.5-1.2 m.
- Peroxisomes contain oxidases and catalase which regulate O2 and H2O2, which could cause irreversible damage to many important cellular constituents.
- The peroxisomal enzymes are synthesized on free ribosomes in the cytoplasm and transferred to peroxisomes.
Cytoskeletal Elements
- The cytoplasm contains a complex network of microtubules, microfilaments, and intermediate filaments.
- These elements form the cytoskeleton, which is responsible for promoting movement and maintaining the shape and organization of the cell.
Cytoskeletal Element Functions
- Cytoskeletal elements:
- Maintain and change the cell's shape
- Produce cell movements
Cytoskeletal Element Types
- Cytoskeletal element types:
- Microfilaments (e.g., actin)
- Intermediate filaments (many)
- Thick filaments (myosin)
- Microtubules: 13 protofilaments, containing polymers of tubulin proteins.
Microtubules
- Microtubules, in addition to their role in the cytoskeleton, form specialized structures like cilia, flagella, centrioles, and basal bodies.
Centrioles
- Centrioles are cylindrical organelles (0.15 m in diameter & 0.3-0.5 m in length).
- Centrioles have nine peripheral triplets of microtubules arranged in a pinwheel fashion.
- Centrioles form the microtubules of mitotic spindles.
Cilia and Flagella
- Cilia and flagella are movable organelles with a highly organized microtubule core; they extend from the surface of some cell types.
- Ciliated cells usually possess a large number of cilia (≈ 300) that are 2-10 m long.
- Flagellated cells normally have only one flagellum, which ranges in length from 50 to 200 m.
- Both cilia and flagella have a diameter of 0.2-0.5 m and have the same organized core consisting of nine doublets of microtubules surrounding two central microtubules (9 + 2 pattern, axoneme).
Basal Bodies
- Basal bodies are identical to centrioles and found at the base of each cilium or flagellum.
- The outer microtubule of a triplet ends at the apical end of the basal body, while the other two microtubules of the triplet are continuous with the corresponding microtubules of the ciliary or flagellar axoneme.
- Basal bodies act as a template to control formation of cilia or flagella axoneme.
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Description
This quiz explores the crucial components of the cytoplasm, including its structure, organelles, and the types of endoplasmic reticulum. Dive into the specifics of membranous and non-membranous organelles, and understand their functions within the cell. Perfect for students seeking a deeper understanding of cell biology.
