1.1 (R) - The Eukaryotic Cell

Plasma membrane

A selectively permeable barrier made of a phospholipid bilayer that regulates movement of substances into and out of the cell.

What is the plasma membrane primarily made of?

A phospholipid bilayer.

What are the three parts of a phospholipid?

Fatty acid chains, glycerol backbone, and phosphate group.

What part of a phospholipid is hydrophilic?

The phosphate head.

What part of a phospholipid is hydrophobic?

The fatty acid tails.

What is the function of the plasma membrane?

To regulate passage of substances into and out of the cell.

What are the two main types of transport across membranes?

Active transport and passive transport.

What are microvilli?

Finger-like folds of the plasma membrane that increase surface area for absorption.

Why do microvilli increase absorption?

They increase surface area, allowing more nutrients to be absorbed.

What happens to microvilli in celiac disease?

They are damaged by an immune response to gluten.

What are the consequences of damaged microvilli in celiac disease?

Poor nutrient absorption leading to malnutrition, cramping, and diarrhea.

Cytoplasm

The contents of the cell located between the plasma membrane and nuclear envelope.

What structures are found in the cytoplasm?

Organelles suspended in cytosol and the cytoskeleton.

What substances are dissolved in cytoplasm?

Proteins, glucose, amino acids, and ions.

Why do many metabolic reactions occur in the cytoplasm?

Because it contains dissolved ions and enzymes required for reactions.

Cytoskeleton

A network of protein fibers that maintains cell shape and enables movement of cellular components.

What are the three types of cytoskeleton fibers?

Microfilaments, intermediate filaments, and microtubules.

Microfilaments (actin)

The thinnest cytoskeletal fibers involved in cell movement and structure.

What is the function of microfilaments?

Moving cellular components and maintaining structure of microvilli.

Intermediate filaments

Cytoskeletal fibers that provide mechanical strength and anchor organelles.

What is an example of an intermediate filament protein?

Keratin.

What is the function of keratin?

Strengthens hair, nails, and skin cells.

Microtubules

The thickest cytoskeletal fibers that form hollow tubes used in movement and division.

What is unique about microtubules?

They dissolve and reform quickly.

What is the role of microtubules in cell division?

They separate sister chromatids.

Where are microtubules found besides cytoplasm?

In cilia and flagella.

Flagellum

A long structure that moves an entire cell.

What is an example of a cell with a flagellum?

Sperm cell.

Cilia

Short, numerous structures that move substances across cell surfaces.

What is an example of cells with cilia?

Cells lining the fallopian tube that move the ovum.

Endomembrane system

A group of organelles that modify, package, and transport proteins and lipids.

What organelles are part of the endomembrane system?

Nuclear envelope, ER, Golgi apparatus, lysosomes, and vesicles.

Nucleus

Organelle that houses DNA and controls cell activities.

What form is DNA stored in inside the nucleus?

Chromatin.

Chromatin

A combination of DNA and proteins found in the nucleus.

Chromosomes

Condensed structures of DNA visible during cell division.

What is the nuclear envelope?

A double membrane surrounding the nucleus.

What controls movement through the nuclear envelope?

Nuclear pores.

What is the nucleolus?

A region in the nucleus that assembles ribosomal RNA and ribosome subunits.

Where do ribosomal subunits go after being made in the nucleolus?

Through nuclear pores into the cytoplasm.

Endoplasmic reticulum (ER)

A network of membranes involved in protein and lipid synthesis.

What is the lumen of the ER?

The hollow interior space inside ER tubules.

How is the ER connected to the nucleus?

The ER membrane is continuous with the nuclear envelope.

Rough ER (RER)

ER with ribosomes attached that synthesizes proteins.

What happens to proteins synthesized in the rough ER?

They enter the ER lumen and are modified.

What else does rough ER produce besides proteins?

Phospholipids.

Which cells contain large amounts of rough ER?

Cells that secrete proteins, such as liver cells.

Smooth ER (SER)

ER without ribosomes that synthesizes lipids and carbohydrates.

What substances are produced by smooth ER?

Lipids, carbohydrates, and steroid hormones.

Golgi apparatus (GA)

Organelle that modifies, sorts, tags, and packages proteins and lipids.

What is the receiving side of the Golgi apparatus?

The side facing the ER.

What is the releasing side of the Golgi apparatus?

The side facing the plasma membrane.

What happens to vesicles entering the Golgi?

Their contents are modified and tagged for delivery.

Where do Golgi vesicles go after packaging?

To other organelles or outside the cell.

Which cells have large Golgi apparatuses?

Highly secretory cells such as salivary gland cells.

What does the Golgi apparatus synthesize in plant cells?

Polysaccharides.

Lysosome

A membrane-bound organelle containing digestive enzymes.

Why is the lysosome interior acidic?

Digestive enzymes require low pH to function.

What is the function of lysosomes?

Breaking down macromolecules and pathogens.

How do macrophages use lysosomes?

They engulf pathogens and fuse vesicles with lysosomes to destroy them.

Vesicles

Small membrane-bound sacs that transport substances.

What is unique about vesicles?

They can fuse with membranes.

Vacuoles

Large membrane-bound sacs involved in storage and breakdown.

How do vacuoles differ from vesicles?

Vacuoles are larger and do not typically fuse.

Ribosomes

Structures responsible for protein synthesis.

What are ribosomes made of?

Large and small subunits.

Where are ribosomes found?

In all cells.

Why are ribosomes abundant in red blood cell precursors?

To produce hemoglobin.

Mitochondria

Organelles that produce ATP through cellular respiration.

What type of membrane structure do mitochondria have?

Double membrane.

What are cristae?

Folds of the inner mitochondrial membrane.

Why are cristae important?

They increase surface area for ATP production.

What is the mitochondrial matrix?

The space enclosed by the inner membrane folds.

Which cells contain many mitochondria?

Muscle cells.

Peroxisome

Organelle that carries out oxidation reactions.

What substances are broken down in peroxisomes?

Fatty acids and amino acids.

What toxic substance is produced in peroxisomes?

Hydrogen peroxide (H₂O₂).

How is hydrogen peroxide handled safely in peroxisomes?

It is broken into water and oxygen.

What is a major function of peroxisomes in liver cells?

Detoxifying alcohol and poisons.

What is the thickness of the cell membrane?

Approximately 5–10 nm.

What regulates membrane fluidity?

Cholesterol.

How does cholesterol act in membranes?

As an antifreeze to maintain fluidity.

Why do animals in cold climates have more cholesterol in membranes?

To prevent membranes from becoming too rigid.

Integral proteins

Membrane proteins that span all or part of the membrane.

What are functions of integral proteins?

Channels, pumps, enzymes, or receptors.

Peripheral proteins

Proteins located on the inner or outer membrane surface.

What are carbohydrate chains in membranes attached to?

Proteins or lipids.

Where are carbohydrates found on the membrane?

On the outer surface only.

What is the function of membrane carbohydrates?

Cell-to-cell recognition.

Fluid mosaic model

Describes the membrane as a flexible structure made of moving components.

What components make up the membrane mosaic?

Phospholipids, cholesterol, proteins, and carbohydrates.

Why is the membrane described as fluid?

Components can move laterally within the bilayer.

How do viruses infect specific cells?

Viral glycoproteins bind to specific receptors on host cells.

Why can viruses infect only certain organs?

Only certain cells have matching receptors.

How does the immune system recognize viruses?

By detecting viral surface proteins.

Why is developing vaccines against HIV difficult?

HIV surface proteins change rapidly due to fast-mutating genes.

What are viral variants?

Rapidly evolving viral forms with changed surface proteins.