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Questions and Answers
What is the primary role of the plasma membrane in a prokaryotic cell?
Which of the following correctly describes the bacteria Mycoplasma?
What is the composition of the cell wall in typical bacteria?
What differentiates a capsule from a slime layer in glycocalyx?
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What is the primary function of glycocalyx in bacteria?
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What is a characteristic of prokaryotic DNA?
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Which statement correctly describes plasmids in prokaryotic cells?
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In prokaryotic cells, what is the function of the cell wall?
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Which statement best describes cell theory?
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What is the primary function of a light microscope?
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Which of the following parameters does NOT apply to microscopy?
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Which of the following cell types does NOT possess a membrane-enclosed nucleus?
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What structure is common to all prokaryotic cells?
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Which category of prokaryotic cells is specifically known for thriving in extreme environments?
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Which structure is involved in increasing the genetic diversity of prokaryotic cells?
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What is the resolution capability of an electron microscope?
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What is the primary role of the cytosol in a eukaryotic cell?
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Which of the following statements best describes catabolism?
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What distinguishes microtubules from intermediate filaments?
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How do actin filaments contribute to cellular movement?
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Which function is specifically associated with intermediate filaments?
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What is the dynamic instability characteristic of microtubules?
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In which cellular processes do microtubules play critical roles?
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Which of the following statements accurately describes the cytoskeleton's function?
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What occurs when a peptide sequence contains a stretch of 20 hydrophobic amino acids?
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What is the main role of glycosylation in proteins?
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What distinguishes N-linked glycosylation from O-linked glycosylation?
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How do essential molecules like glucose enter a cell through the plasma membrane?
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Which of the following substances would most likely have difficulty crossing the plasma membrane?
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Where does N-linked glycosylation primarily begin?
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What is the structure associated with the oligosaccharide chain in N-linked glycosylation?
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What type of carbohydrate chain is typically found in O-linked glycosylation?
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What structure forms the basic framework of biological membranes?
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What characteristic allows phospholipids to arrange themselves in a bilayer formation?
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What describes the fluid-mosaic model of membranes?
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Which type of membrane protein is known for being embedded within the hydrophobic region of the phospholipid bilayer?
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What is true about the movement of proteins in the membrane?
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Which region of a phospholipid molecule is hydrophilic?
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What type of diffusion is described when phospholipids move from one leaflet of the membrane to another?
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What role do membrane carbohydrates primarily serve?
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Study Notes
Cell Theory
- All living organisms are composed of one or more cells
- Cells are the smallest units of living organisms
- New cells come only from pre-existing cells by cell division
Microscopy
- Microscopic tools are used to understand the structure and function of cells
- Magnification, resolution, and contrast are important parameters in microscopy
- Magnification: Ratio of the size of an image produced by a microscope and its actual size
- Resolution: Ability to observe two adjacent objects as distinct from one another
- Contrast: The ability to visualize a particular cell structure may depend on how different it looks from an adjacent structure. Contrast can be enhanced using dyes.
- Two types of microscopes based on illumination:
- Light Microscopes: Use light for illumination. They have a resolution of 0.2 µm.
- Electron Microscopes: Use an electron beam for illumination. They have a much better resolution of 2 nm.
Cell Types
- Based on cell structure, there are two types of cells:
- Prokaryotic: Simple cell structures lacking a membrane-enclosed nucleus. These cells are much smaller than eukaryotic cells and are present in great numbers in the air, water, soil and even in the human body. There are two categories of prokaryotes: bacteria and archaea.
- Eukaryotic:
Prokaryotic Cells
- Prokaryotic cells contain:
- Cell wall
- Cell membrane
- Cytoplasm
- DNA
- Ribosomes
- Additional structures found in some prokaryotic cells:
- Capsule
- Plasmids
- Flagella
- Pili
- Membrane infolding
Prokaryotic Cell Structure: The Cell Envelope
- The cell envelope includes the plasma membrane, cell wall, and glycocalyx (a layer of polysaccharides outside the cell wall).
- Plasma membrane: A phospholipid bilayer similar to the plasma membrane of eukaryotic cells. It plays an important role in regulating the entrance and exit of substances into the cytoplasm.
- Cell wall: Composed of peptidoglycan (amino disaccharides and peptide fragments). The cell wall maintains the overall shape of a bacterial cell (coccus, bacillus, and spiral). Mycoplasma are bacteria that lack a cell wall and have no definite shape.
- Glycocalyx: A layer of polysaccharide lying outside the cell wall. Glycocalyx helps against drying out by trapping water and assists bacteria in resisting a host’s immune system. It allows the bacterium to attach itself to inert surfaces (like teeth or rocks), eukaryotes (e.g., streptococcus pneumoniae attaches itself to lung cells), or other bacteria (their glycocalyxes can fuse to envelop the colony).
Prokaryotic Cell Structure: Glycocalyx or Capsule
- When glycocalyx is firmly attached, it is called a capsule, otherwise it is a slime layer.
- It is a well-organized layer of polysaccharide.
- It protects the bacterial cell and is often associated with pathogenic bacteria because it serves as a barrier against phagocytosis by white blood cells.
- It is made from starch or glycolipid.
- It helps to protect bacteria from drying out (desiccation).
- It helps to stop detection from the immune system.
- It also protects against viruses.
- It has adhesion properties.
Prokaryotic Cell Structure: Inside the Cell
- No nucleus: The nucleoid floats in the cytoplasm.
- One chromosome: The chromosome is circular.
- No histone proteins: DNA is called naked DNA because there are no histone proteins associated with it.
Prokaryotic Plasmid
- Smaller circular DNA
- Contains resistance genes, which can be transferred to other organisms.
- Non-essential genes
- Replication is independent of chromosomal DNA.
Cytosol
- The region of a eukaryotic cell that is outside the cell organelles but inside the plasma membrane.
- Cytoplasm includes everything inside the plasma membrane: the cytosol, the endomembrane system and the semiautonomous organelles.
- Cytosol is the central coordinating region for many metabolic activities of eukaryotic cells.
- Catabolism: Breakdown of a molecule into smaller components.
- Anabolism: Synthesis of cellular molecules and macromolecules.
Cytoskeleton
-
Serves as an internal skeleton that maintains cell shape (construction and organization) and assists in the movement of its parts. It strengthens the cell and holds organelles in place. There are three types:
-
Microtubules: Long cylindrical structures composed of polymers of alpha and beta tubulin.
- Alpha and beta subunits form a dimer, which pairs with each other to form a sheet-like structure, which is further folded into a cylinder-shaped structure.
- They have a polar structure, with a plus end and a minus end.
- A single microtubule can oscillate between growing and shortening phases: dynamic instability.
- They play key roles in:
- Intracellular transport (associated with dyneins and kinesins, they transport organelles like mitochondria or vesicles).
- The axoneme of cilia and flagella.
- The mitotic spindle.
- Synthesis of the cell wall in plants.
-
Intermediate filaments: Tend to be more stable than microtubules and actin filaments, which readily polymerize and depolymerize.
- They function in the maintenance of cell shape and rigidity by bearing tension.
- They are found in the cytoplasm, in the nucleus, and also outside of the cell, binding cells together.
- Composed of keratin family proteins.
-
Actin filaments: Composed of two intertwined actin chains (also known as microfilaments).
- Actin filaments support the plasma membrane and provide strength and shape to the cell.
- Participate in some cell-to-cell or cell-to-matrix junctions.
- Involved in phagocytosis.
- Provide tensile strength.
-
Cytoskeleton Function
- Maintaining cell shape
- Microfilament: Cytoplasmic streaming. Circulating cytosol so that all organelles receive cytoplasm. Cytokinesis of animal cells. Helps in cell division.
- Microtubule: Segregation of chromosomes during cell division (anaphase). Interacts with centromere for separating sister chromatids. Helps in motility. Are part of flagella, cilia.
- Intermediate filament: Helps in forming stable tissues.
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Description
Test your knowledge on the fundamentals of cell theory, including the composition and division of cells. Explore the principles of microscopy, including magnification, resolution, and contrast, to understand how cells are observed. This quiz also covers the different types of microscopes used in biological studies.