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Questions and Answers
What is the basic structural and functional unit of the body?
cell
Which of the following are parts of the cell? (Select all that apply)
The cell membrane is impermeable to all substances.
False
The cell membrane is made up of ____ percent proteins.
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What are the three types of lipids found in the cell membrane?
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What is the role of cholesterol in the cell membrane?
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What are lysosomes responsible for?
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The cell nucleus is considered the smallest organelle.
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Which function is NOT associated with integral proteins in the cell membrane?
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What is the cell?
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What are the three principal parts of a cell?
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The cell membrane is impermeable to all substances.
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What percentage of the cell membrane is made up of proteins?
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Which type of lipid is a major component of the cell membrane?
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What is the function of membrane cholesterol?
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What type of proteins are embedded throughout the cell membrane?
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What are lysosomes responsible for?
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The cytoplasm contains a jelly-like matrix within the cell where cell organelles are suspended known as _____ .
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Which structure contains the genetic material of the cell?
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Study Notes
The Cell
- The cell is the fundamental building block of life and the functional unit of all living organisms.
- Cells are responsible for carrying out a wide variety of tasks essential for life.
- Every organ in the body functions as a result of the combined activity of the cells that compose it.
Cell Membrane
- The cell membrane is a thin, flexible, and elastic barrier that encloses the cell's cytoplasm.
- It's responsible for separating and protecting the internal environment of the cell.
- The membrane is selectively permeable, meaning it allows some substances to pass through while blocking others.
Composition of the Cell Membrane
- The cell membrane is composed primarily of lipids (55% proteins, 42% lipids, 3% carbohydrates).
Lipids
- The lipid portion is organized as a phospholipid bilayer.
- The phospholipid bilayer has a hydrophilic (water-loving) phosphate head and a hydrophobic (water-fearing) fatty acid tail.
- Cholesterol is dissolved within the lipid bilayer, contributing to membrane stability and fluidity.
- Glycolipids are carbohydrates bound to the outer surface of the membrane, playing a role in cell-cell recognition.
Proteins
- Integral proteins span the entire membrane, serving as channels for water-soluble substances, carrier proteins for transport, and receptors for various signaling molecules.
- Peripheral proteins are attached to either the inner or outer surface of the membrane and act as enzymes or contribute to transport.
Carbohydrates
- Carbohydrates mostly exist as glycolipids and glycoproteins found on the outer surface of the membrane, forming the glycocalyx.
- The glycocalyx participates in cell-cell recognition, stabilization of membrane structure, immune responses, and various cell functions.
Cytoplasm and Organelles
- Cytoplasm is the gel-like substance within the cell that houses various organelles.
- It contains a network of microtubules and microfilaments, mainly composed of Actin, forming the cytoskeleton which provides structure and support.
Lysosomes
- Lysosomes are membrane-bound organelles that play a critical role in cellular digestion.
- They contain digestive enzymes that breakdown nutrients, harmful molecules, and old organelles.
- Lysosomes contribute to a process called autophagy, the breakdown of worn-out organelles, ensuring continuous renewal.
- Lysosomes are also involved in apoptosis, the programmed cell death process.
Cell Structure and Functions
- The cell is the fundamental building block of the body, responsible for all the functions of every organ.
- Cells consist of three primary parts:
- Plasma membrane
- Cytoplasm and organelles
- Nucleus
Cell Membrane
- The cell membrane is a thin, flexible barrier surrounding the cell's cytoplasm.
- Key characteristics:
- 75-100 angstroms thick
- Elastic
- Semipermeable (selective permeability)
- Fluid
Functions of the Cell Membrane
- Acts as a selective barrier controlling the passage of substances into and out of the cell.
- Protects the cytoplasm and maintains the cell's internal environment.
- Regulates substance transport.
- Contains protein receptors for hormones and neurotransmitters.
- Houses numerous regulated ion channels.
- Connects adjacent cells and to the extracellular matrix.
- Generates the membrane potential in excitable cells (nerve and muscle).
Cell Membrane Composition
- Contains three main components:
- 55% proteins
- 42% lipids
- 3% carbohydrates
Lipids in the Cell Membrane
- Form a continuous layer throughout the membrane.
- Three types:
- Phospholipids bilayer
- Dissolved cholesterol
- Glycolipids
Phospholipid Bilayer
- Composed of phospholipid molecules.
- One end (phosphate group) is hydrophilic (water-soluble).
- The other end (fatty acid portion) is hydrophobic (fat-soluble).
- Responsible for the selective permeability of the cell membrane (prevents the passage of water and water-soluble molecules but allows the passage of fat-soluble molecules).
- Contributes to the membrane's fluidity.
Cholesterol
- Located on the inner side of the cell membrane between the phospholipid heads dissolved in the lipid bilayer.
- Functions:
- Provides strength and solidity to the cell membrane.
- Contributes to membrane permeability and fluidity, similar to the phospholipid bilayer.
Glycolipids
- Carbohydrate molecules attached loosely to the outer surface of the membrane, connected to the phosphate group.
- Present on the outer surface of the cell membrane creating a thin layer called glycocalyx.
Functions of Glycolipids and Glycoproteins:
- Act as markers aiding in cell-cell recognition.
- Stabilize membrane structure.
- Participate in immune reactions, distinguishing self from non-self.
- Contribute to cell adhesion through interactions with other cells.
- Serve as receptors for hormones and neurotransmitters.
- Function as antigens like those of the ABO system on red blood cells.
- Function as enzymes facilitating biochemical reactions at the cell surface.
Cell Membrane Proteins
- Two types:
- Integral proteins
- Peripheral proteins
Integral Proteins
- Extend all the way through the membrane.
- Functions:
- Provide structural channels (pores) for water-soluble substances (ions).
- Act as carrier proteins, transporting substances that cannot penetrate the membrane.
- Facilitate active transport, moving substances against their natural diffusion direction.
- Serve as receptors for water-soluble chemicals.
- Function as enzymes, facilitating biochemical reactions at the cell surface.
Peripheral Proteins
- Attached to only one surface of the membrane, not penetrating the membrane.
- Functions:
- Primarily function as enzymes.
- Regulate the transport of substances through the cell membrane.
Cytoplasm and Organelles
- Cytoplasm:
- Is the aqueous content of the cell.
- Contains a well-organized internal structure with microtubules and microfilaments (mainly Actin), which act as a cytoskeleton.
- Organelles:
- Are subcellular structures suspended within the cytoplasm.
- Nucleus:
- Is the largest organelle within the cell.
- Contains the genetic material (DNA).
Lysosomes
- Responsible for:
- Digestion: contain digestive enzymes for breaking down nutrients and harmful molecules.
- Autophagy: remove worn-out (old) organelles for continuous replacement.
- Apoptosis (programmed cell death): release digestive enzymes into the cell, initiating programmed cell death.
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Description
Explore the fundamental building blocks of life with this quiz on cells and their structures. Learn about the cell membrane's composition and its vital role in protecting the cell's internal environment. Test your knowledge on the components that make up cell membranes and their functions.
