Biology Quiz on Cell Structures and Functions

Cytology

• Cytology is the branch of biology and medicine that studies cell structure and function.
• All living organisms are made up of cells.
• The cell is the basic unit of structure and function in multicellular organisms.
• In unicellular organisms, the single cell performs all life functions.

Comparison between Prokaryotes and Eukaryotes

• Most prokaryotes are unicellular.
• Prokaryotic nuclei are poorly defined, lacking a nuclear membrane.
• Prokaryotic cells lack a nucleolus.
• Prokaryotic cells lack membrane-bound organelles like mitochondria, plastids, and Golgi bodies.
• Bacteria and blue-green algae are prokaryotes.
• Most eukaryotes are multicellular.
• Eukaryotic nuclei have a well-defined nuclear membrane.
• Eukaryotic cells contain a nucleolus.
• Eukaryotic cells contain membrane-bound organelles like mitochondria, plastids, and Golgi bodies.
• Fungi, plant, and animal cells are eukaryotes.

Level of Organization

• The biological levels of organization of living things range from organelles to cells to tissues to organs to organ systems to organisms.
• These levels are arranged from the simplest to most complex.

Chemical Structure of the Cell

• Water makes up about 70% of cell weight.
• Water acts as a solvent for biochemical reactions.
• Organic materials include carbohydrates, lipids, proteins, and nucleic acids.
• Inorganic materials include minerals like calcium, phosphate, sodium, and magnesium ions.
• Other minerals like cobalt, copper, iron, iodine, manganese, and zinc are also important.

Carbohydrates

• Carbohydrates have the general formula (CnH2nOn), where n is an integer between 3 and 7.
• Carbohydrates are classified into monosaccharides, oligosaccharides, and polysaccharides.
• Monosaccharides are single sugar molecules (e.g., glucose, fructose, galactose).
• Oligosaccharides have between two and ten sugar molecules (e.g., sucrose, lactose, maltose).
• Polysaccharides have more than ten sugar molecules (e.g., starch, glycogen, cellulose).
• Carbohydrates can be linked together by glycosidic linkages.
• Carbohydrates can bond with proteins to form glycoproteins and bond with lipids to form glycolipids.

Lipids

• Lipids include fats, phospholipids, and steroids.
• Lipids are major structural components of cells.
• The simplest unit of lipids are fatty acids.
• Fatty acids have a long hydrocarbon chain and a carboxylic group.
• The hydrocarbon chain is hydrophobic (water-insoluble).
• The carboxylic group is hydrophilic (water-soluble) and chemically reactive.

Proteins

• Proteins are major structural components of cells.
• The fundamental unit of proteins is amino acids.
• Amino acids have a carboxyl group and an amino group.
• Amino acids are linked together by peptide bonds.
• About 20 amino acids occur naturally.

Nucleic Acids

• Nucleic acids are the genetic material of the body, including DNA and RNA.
• The building blocks of nucleic acids are nucleotides.
• Nucleotides consist of a phosphate group, a deoxyribose sugar, and a nitrogenous base.
• Nitrogenous bases are classified into purines (adenine, guanine) and pyrimidines (cytosine, thymine, uracil).

Animal Cell Structure

• All cells are enclosed by a plasma membrane which acts as a selective barrier.
• The interior of the cell is organized into organelles, specialized compartments.
• Organelles, such as the nucleus, mitochondria, lysosomes, endoplasmic reticulum, and Golgi apparatus, are surrounded by a separate membrane.
• Organelles are suspended in the cytoplasm, or cytosol.

Plasma Membrane

• The plasma membrane is a thin membrane, roughly 5 nanometers thick, surrounding living cells.
• It forms a selective barrier, regulating the passage of substances into and out of the cell.
• Functions as a barrier to keep substances within the cell and keep unwanted substances out.
• Allows transport of nutrients and waste products in and out of the cell.
• Composed mostly of lipids and proteins.
• Lipids form a phospholipid bilayer.
• Proteins are embedded within the lipid bilayer, including both peripheral and integral proteins.
• Sterols, such as cholesterol, are also part of the membrane.

Phospholipid Bilayer

• Phospholipids have a glycerol head and two hydrocarbon tails.
• The head is attached to a phosphoryl group, which carries a negative charge.
• The tails are hydrophobic and repel water.
• The phospholipid bilayer forms a barrier, with the hydrophobic tails facing inward and the hydrophilic heads facing outward.

Sterols

• Sterols have a complex hydrocarbon ring structure to act as lipid-soluble parts.
• They have a hydroxyl (OH) group to act as the water-soluble part.
• Cholesterol is the primary example.

Membrane Proteins

• Membrane proteins are of two types: peripheral and integral.
• Peripheral proteins are loosely attached to the membrane surface.
• Integral proteins are firmly embedded within the membrane.
• Many integral proteins extend through the entire membrane.
• Integral proteins often contain amino acid sequences that span the membrane, allowing them to bind to the interior region.
• Some intrinsic proteins have side chains of complex sugars that participate in cell-to-cell recognition.

Transport Across the Plasma Membrane

• Transport across the plasma membrane includes passive processes (diffusion, facilitated diffusion) and active transport.
• Passive transport involves movement down a concentration gradient without energy expenditure.
• Active transport requires energy to move substances against their concentration gradient.

Permeation

• Permeation or simple diffusion involves the movement of small lipid-soluble molecules and substances across the membrane.
• Large, water-soluble molecules and electrically charged ions do not permeate the membrane easily.
• Examples of substances that permeate by simple diffusion include oxygen and alcohols.

Facilitated Diffusion

• Facilitated diffusion is a passive transport process that moves substances across the membrane using specific channels or transporters in the membrane.
• The substances move down their concentration gradient.
• Channels are integral proteins forming holes or pores in the membrane, allowing specific ions to pass through.
• Channels can open and close spontaneously or be gated.
• Transporters are intrinsic (integral proteins) with a high specificity binding site.

Active Transport

• Active transport requires energy (ATP hydrolysis) to move substances against their concentration gradient using specific pumps in the cell membrane.
• The sodium-potassium pump is an example of an active transport mechanism.

Transport of Particles

Large molecules such as proteins and nucleic acids cannot cross the plasma membrane by simple diffusion.

• These large molecules are internalized by endocytosis and externalized by exocytosis.

Ribosomes

• Ribosomes are particles that synthesize proteins from amino acids.
• Ribosomes consist of rRNA and protein assembled into large and small subunits.
• Ribosomes can be free in the cytoplasm or bound to the endoplasmic reticulum.
• Lysosomal enzymes and proteins to be secreted from the cell are synthesized on ribosomes.

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum is a system of membranous vesicles extending throughout the cytoplasm.
• Two types of ER exist: smooth ER and rough ER.
• Rough ER has ribosomes attached to its surface.
• Rough ER is involved in protein synthesis, secretion, and glycosylation.
• Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and steroid hormone production.

Golgi Apparatus

• The Golgi apparatus is a series of flattened membranous sacs (cisternae).
• Two faces of the Golgi apparatus exist, the cis and trans faces.
• Cis face faces the nucleus.
• Trans face faces the plasma membrane.
• The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

Lysosomes

• Lysosomes are membrane-bound organelles containing digestive enzymes.
• Lysosomes hydrolyze proteins, nucleic acids, lipids, glycolipids, and glycoproteins.
• Lysosomes break down worn-out organelles and materials from inside or outside the cell.

Mitochondria

• Mitochondria are organelles known as the powerhouses of the cell.
• Mitochondria are long, slender, and oval-shaped organelles.
• Mitochondrion has outer and inner membranes.
• The outer membrane is smooth but the inner membrane has infoldings called cristae.
• Mitochondrial matrix contains enzymes and proteins crucial for oxidative phosphorylation, where ATP (energy) is produced.

Cytoskeleton

• The cytoskeleton is a fibrous protein network that provides a framework for the cell.
• It organizes cell components and maintains cell shape.
• Microfilaments, microtubules, and intermediate filaments are three major types of cytoskeletal filaments.

Centrosomes

• Centrosomes are spherical structures containing centrioles.
• Centrosomes are located near the nucleus of animal, fungal, and algal cells.
• During cell division, centrosomes divide, and each centrosome moves to opposite poles of the cell.
• Centrioles organize microtubules in the spindle apparatus, involved in chromosome separation during cell division.

Nucleus

• The nucleus is the control center of the cell.
• It contains genetic material that's passed on to offspring.
• Each nucleus consists of a nuclear envelope, nuclear pores, nucleoplasm, nucleolus, and chromatin.
• The nucleus is crucial for DNA replication and storage.

Chromosomes

• Chromosomes are aggregates of DNA and proteins (histones).
• Genes are located on specific regions of chromosomes.
• Most organisms have two sets of paired chromosomes (diploid), inheriting one set from each parent.
• During S phase, chromosomes replicate in preparation for cell division.
• The replicated chromosomes form a characteristic X-shaped structure (metaphase chromosome).