Questions and Answers
What is the main function of the cell membrane in human cells?
Which of the following cell types is known to lack a nucleus when mature?
What structural feature is primarily responsible for the selective permeability of the cell membrane?
Which type of protein is mostly found within the phospholipid bilayer and spans the membrane?
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What role does cholesterol play in the cell membrane?
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What role do membrane proteins play in the transport of small water-soluble substances across the cell membrane?
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Which of the following describes the primary function of the nucleus in human cells?
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What is the function of carrier proteins found in membrane proteins?
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Which component is NOT typically found in the structure of the nucleus?
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How do enzymes associated with membrane proteins function in cellular activities?
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Study Notes
Cell Overview
- Cells are the smallest living units in the human body, which is multicellular.
- Human cells rely on each other, unlike microorganisms like bacteria that operate independently.
- Cell sizes vary, mostly observed under a microscope, measured in micrometers (1 μm = 1/1,000,000 m).
- The human ovum is the exception, visible to the naked eye.
Cell Structure
- Human cells share common features: cell membrane, nucleus, cytoplasm, and organelles.
- Red blood cells uniquely lack a nucleus and organelles when mature.
Cell Membrane
- Also known as the plasma membrane, surrounds the cytoplasm and organelles.
- Composed of phospholipids, cholesterol, and proteins, with a double-layer structure allowing selective permeability.
- Cholesterol stabilizes the membrane by reducing its fluidity.
Membrane Proteins
- Two types:
- Integral (transmembrane) proteins, often glycoproteins.
- Peripheral proteins, mostly on the inner membrane surface.
- Functions include:
- Channels for small molecules (e.g., sodium, potassium).
- Carriers for larger water-soluble substances.
- Antigens for identifying the body’s cells.
- Receptors for hormones initiating physiological responses.
- Enzymes that can terminate hormone effects.
Nucleus
- Found in all human cells except mature red blood cells.
- Enclosed by a double-layer nuclear membrane with pores and contains nucleoli and chromosomes (46 total).
- The nucleolus produces ribosomal RNA, essential for protein synthesis.
- The nucleus controls cellular functions by housing genetic material (DNA).
Cytoplasm and Organelles
- Cytoplasm consists of minerals, gases, organic molecules, and organelles.
- Cytosol is the water portion of cytoplasm without organelles.
- Organelles perform specific functions:
-
Endoplasmic Reticulum (ER):
- Rough ER has ribosomes for protein synthesis.
- Smooth ER synthesizes lipids.
- Ribosomes: Site for protein synthesis made of protein and ribosomal RNA.
- Proteasomes: Degrade unneeded or damaged proteins.
-
Endoplasmic Reticulum (ER):
Additional Organelles
- Golgi Complex: Modifies, sorts, and packages proteins and lipids for transport.
-
Mitochondria:
- Double-membraned, site of ATP production through aerobic respiration.
- Contains maternal mitochondrial DNA and duplicates during cell division.
- Lysosomes: Contain digestive enzymes for degrading bacteria engulfed by white blood cells.
- Centrioles: Organize spindle fibers during cell division, located perpendicular to each other.
Cellular Projections
- Cilia: Short, numerous projections that move materials across the cell surface (e.g., in fallopian tubes).
- Flagella: Long, singular projection aiding in movement, exemplified by sperm cells.
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Description
Explore the fundamental building blocks of life in this quiz on cell physiology. Understand the differences between human cells and microorganisms, along with their sizes, shapes, and functions. Test your knowledge on how cells work together to support the human body.
