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Questions and Answers
Which organelle is known as the powerhouse of the cell and is surrounded by a membrane?
Which organelle is known as the powerhouse of the cell and is surrounded by a membrane?
All cells have membranous organelles.
All cells have membranous organelles.
False
What is the primary function of the cytoskeleton?
What is the primary function of the cytoskeleton?
To shape, stabilize, and move cells and their internal structures.
The plasma membrane is described as a ________ that regulates the exchange of materials with the environment.
The plasma membrane is described as a ________ that regulates the exchange of materials with the environment.
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Match the following components with their respective functions:
Match the following components with their respective functions:
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What are the primary components of cilia and flagella?
What are the primary components of cilia and flagella?
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The nucleus contains all of the information necessary to synthesize cellular proteins.
The nucleus contains all of the information necessary to synthesize cellular proteins.
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What structures are responsible for manufacturing ribosomal subunits in the nucleus?
What structures are responsible for manufacturing ribosomal subunits in the nucleus?
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The _______ endoplasmic reticulum synthesizes lipids, including fatty acids and steroids.
The _______ endoplasmic reticulum synthesizes lipids, including fatty acids and steroids.
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Which organelle is responsible for modifying and sorting proteins for export?
Which organelle is responsible for modifying and sorting proteins for export?
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Match the following organelles with their primary function:
Match the following organelles with their primary function:
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Transcription occurs in the cytoplasm, while translation takes place in the nucleus.
Transcription occurs in the cytoplasm, while translation takes place in the nucleus.
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What is the primary function of mitochondria?
What is the primary function of mitochondria?
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The inner mitochondrial membrane is folded to form cristae.
The inner mitochondrial membrane is folded to form cristae.
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Name the process that begins with glycolysis and ends with ATP synthesis.
Name the process that begins with glycolysis and ends with ATP synthesis.
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During the S phase, DNA is __________ in preparation for mitosis.
During the S phase, DNA is __________ in preparation for mitosis.
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Which phase of the cell cycle is characterized by the duplication of cytoplasmic components?
Which phase of the cell cycle is characterized by the duplication of cytoplasmic components?
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Match the following phases of mitosis with their correct descriptions:
Match the following phases of mitosis with their correct descriptions:
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Telomeres are pieces of DNA at the ends of chromosomes.
Telomeres are pieces of DNA at the ends of chromosomes.
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Mitosis produces four identical daughter cells.
Mitosis produces four identical daughter cells.
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What is the role of telomerase in cell division?
What is the role of telomerase in cell division?
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What percentage of the membrane is composed of phospholipids?
What percentage of the membrane is composed of phospholipids?
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Saturated fatty acids increase the fluidity of the membrane.
Saturated fatty acids increase the fluidity of the membrane.
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What role does cholesterol play in the fluidity of the membrane?
What role does cholesterol play in the fluidity of the membrane?
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The ability of the lipid bilayer to move proteins and lipids laterally within the layer is defined as ______________.
The ability of the lipid bilayer to move proteins and lipids laterally within the layer is defined as ______________.
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Match the following types of membrane proteins with their descriptions:
Match the following types of membrane proteins with their descriptions:
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Which type of transport is used for nonpolar substances to cross membranes?
Which type of transport is used for nonpolar substances to cross membranes?
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The membrane is highly permeable to polar molecules like glucose.
The membrane is highly permeable to polar molecules like glucose.
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What happens to the rate of diffusion when temperature increases?
What happens to the rate of diffusion when temperature increases?
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Facilitated diffusion requires the help of __________ proteins to transport charged substances.
Facilitated diffusion requires the help of __________ proteins to transport charged substances.
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Study Notes
Cell Structure and Function
- Cells are the basic units of life, exhibiting diverse shapes and functions. The human body contains approximately 200 different cell types.
- Eukaryotic cells possess membrane-bound organelles, while prokaryotic cells do not.
- Organelles are specialized subunits within cells, each with a specific function. Some are membrane-bound (e.g., mitochondria), others are not (e.g., ribosomes).
Plasma Membrane and Cytoplasm
- The plasma membrane is a flexible barrier regulating the exchange of materials between the cell and its environment and facilitating cell communication.
- The cytoplasm, encompassing the area between the plasma membrane and nucleus, provides an aqueous environment for cellular processes.
- The cytoskeleton, composed of microfilaments (actin and myosin), intermediate filaments (various proteins), and microtubules (tubulin), maintains cell shape, stabilizes organelles, and facilitates cell movement. Microfilaments aid cell movement and support; intermediate filaments have high tensile strength and anchor organelles; microtubules are dynamic and involved in chromosome segregation during cell division, cilia, and flagella formation.
Centrosome, Cilia, and Flagella
- The centrosome, the microtubule-organizing center in animal cells, contains centrioles and is crucial for mitotic spindle formation during cell division.
- Cilia, short bundles of microtubules, move fluids surrounding cells (e.g., respiratory tract, oviduct).
- Flagella, longer microtubule bundles, propel cells (e.g., sperm).
Nucleus and DNA
- The nucleus, a double-membraned organelle (nuclear envelope), contains DNA and a nucleolus. Nuclear pores regulate the passage of molecules (e.g., mRNA, ribosomal subunits).
- The nucleolus is responsible for ribosomal subunit assembly. DNA exists as chromatin (loose and accessible for transcription) or chromosomes (tightly wound, genes inaccessible). The genome encompasses all of an organism's DNA.
Ribosomes and the Central Dogma
- Ribosomes, composed of rRNA and protein, translate mRNA into proteins. Ribosomal subunits assemble in the cytoplasm, some attaching to the rough endoplasmic reticulum (rER).
- The central dogma of biology describes the flow of genetic information: DNA (genes) → mRNA → protein. Transcription occurs in the nucleus; translation occurs at ribosomes.
Endoplasmic Reticulum and Golgi Complex
- The endoplasmic reticulum (ER) is a network of membranes involved in protein synthesis and lipid metabolism.
- The rER, studded with ribosomes, synthesizes proteins for organelles and exports membranes.
- The smooth ER (sER) synthesizes lipids, inactivates drugs, participates in carbohydrate metabolism, and stores calcium ions.
- The Golgi complex modifies, sorts, and packages proteins for transport to their destinations. Proteins enter at the entry face and exit at the exit face within the cisternae.
Lysosomes, Peroxisomes, and Proteasomes
- Lysosomes, membrane-bound sacs containing digestive enzymes, break down cellular molecules; defects can lead to lysosomal storage disorders (e.g., Tay-Sachs disease).
- Peroxisomes, containing oxidases and catalase, metabolize fatty acids, detoxify molecules, and process metabolic byproducts.
- Proteasomes, large cytoplasmic complexes, degrade polypeptides into smaller peptides; defects link to diseases like Parkinson's and Alzheimer's.
Mitochondria and Cellular Respiration
- Mitochondria, enclosed by two membranes (inner and outer), perform aerobic cellular respiration. The inner membrane folds (cristae) increase surface area.
- Aerobic cellular respiration (glycolysis in the cytoplasm, ATP synthesis in the mitochondria) converts glucose into ATP in the presence of oxygen: C6H12O6 + 6O2 → 6CO2 + 6H2O + 36-38 ATP.
- Mitochondria are maternally inherited, possess their own DNA, and play a role in apoptosis (programmed cell death).
Cell Division: Mitosis and Cytokinesis
- Somatic cells divide via mitosis (nuclear division) and cytokinesis (cytoplasmic division).
- The cell cycle consists of interphase (G1 – growth, S – DNA replication, G2 – cytoplasmic component replication) and M phase (mitosis).
- Mitosis phases: prophase (nuclear envelope dissolution, chromosome condensation), metaphase (chromosome alignment at the equatorial plate), anaphase (chromosome separation), telophase (partitioning).
- DNA replication is semi-conservative; DNA polymerase uses one strand as a template to create a new complementary strand.
Chromosome Structure and Telomeres
- A replicated chromosome has two sister chromatids joined at the centromere. The kinetochore, a protein complex around the centromere, attaches to the mitotic spindle.
- Telomeres, DNA sequences at chromosome ends, prevent chromosome shortening and degradation. Telomerase adds to telomeres; shortened telomeres are associated with aging and cell death, while cancer cells often have overactive telomerase.
Cell Division: Meiosis
- Meiosis produces gametes (haploid cells) via two successive divisions: meiosis I (separation of homologous chromosomes, crossing over) leads to two non-identical daughter cells, and meiosis II (sister chromatid separation) yields four non-identical haploid gametes.
Membrane Structure and Function
- The fluid mosaic model describes the membrane's fluidity (lateral movement of lipids and proteins) and mosaic nature (diverse components).
- The lipid bilayer, composed primarily of phospholipids (75%), cholesterol (20%), and glycolipids (5%), forms a selective barrier. Cholesterol acts as a fluidity buffer.
- Membrane fluidity depends on fatty acid saturation (unsaturated = more fluid) and temperature.
Membrane Transport
- Selective permeability allows only certain solutes to cross the membrane. Nonpolar molecules passively diffuse across the lipid bilayer.
- Facilitated diffusion, passive transport assisted by membrane proteins, transports polar molecules down concentration gradients (ion channels, carrier proteins).
- Active transport uses energy (ATP) to move substances against concentration gradients. The electrochemical gradient considers both concentration and electrical differences.
Active Transport
- Moves solutes against their concentration gradients.
- In animal cells, the sodium-potassium (Na+-K+) pump maintains higher Na+ concentration outside and higher K+ concentration inside the cell.
- The Na+-K+ pump is a primary active transporter utilizing ATP hydrolysis.
- Secondary active transporters use electrochemical gradients established by primary active transporters.
- Secondary active transporters move two solutes simultaneously; one down its gradient, powering the other up its gradient.
- Symporters move both solutes in the same direction, while antiporters move them in opposite directions.
- Cyanide inhibits ATP production, halting all active transport.
Vesicular Transport
- Vesicles transport products between organelles.
- Endocytosis moves substances into cells.
- Exocytosis moves substances out of cells (secretion).
- Both require ATP hydrolysis.
- Transcytosis involves endocytosis followed by exocytosis, moving substances through cells.
- Receptor-mediated endocytosis imports specific molecules.
- Phagocytosis is engulfing and digesting molecules or invaders; crucial for immune cells.
- Pinocytosis (bulk-phase endocytosis) imports dissolved solutes; important for immune surveillance.
Osmosis and Water Transport
- Water moves from low to high solute concentration.
- Osmosis is water movement across a semi-permeable membrane.
- Water, though small and polar, crosses lipid bilayers inefficiently.
- Aquaporins are channel proteins that facilitate efficient water diffusion across membranes.
Tonicity and Cell Behavior
- Hypertonic solutions have higher solute concentration than the cell; water moves out.
- Hypotonic solutions have lower solute concentration than the cell; water moves in.
- Isotonic solutions have equal solute concentration; no net water movement.
- IV fluids are usually isotonic to maintain osmotic balance.
- Osmolarity is the total solute concentration of a solution; determines tonicity.
Cell Division
- Somatic cells divide via mitosis, producing two identical daughter cells.
- Reproductive cells divide via meiosis, producing four nonidentical gametes.
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Description
Test your knowledge on the fundamental structures and functions of cells. This quiz covers cellular types, organelles, the plasma membrane, cytoplasm, and the cytoskeleton. Gain insights into how these components work together to maintain life.
