Chapter 07: Cell Structure and Function

Comprehensive Question and Answer flashcards reviewing cell structures, organelles, microscopy, fractionations, endomembrane system, energy-converting organelles, cytoskeleton, extracellular matrix, and cellular junctions from Chapter 07.

What three parameters determine how effectively a microscope visualizes a specimen?

Magnification (the ratio of an object's image size to its real size), Resolution (the measure of clarity or minimum distance between two distinguishable points), and Contrast (visible differences in brightness between parts of the sample).

What is the maximum effective magnification of a standard light microscope?

Approximately $1{,}000 \times$ the size of the actual specimen.

What is the primary operational difference between a scanning electron microscope (SEM) and a transmission electron microscope (TEM)?

A scanning electron microscope (SEM) focuses a beam of electrons onto the surface of a specimen to provide 3-D images, whereas a transmission electron microscope (TEM) focuses a beam of electrons through a specimen to study internal cellular structures.

What advantage does cryo-electron microscopy (cryo-EM) offer in structural biology?

It allows preservation and visualization of specimens at very low temperatures in their cellular environment without requiring chemical preservatives.

In differential centrifugation, what cellular components are collected in the pellet after spinning a homogenate at $1{,}000\,g$ for $10\,\text{min}$?

Nuclei and cellular debris.

What four basic features are shared by all prokaryotic and eukaryotic cells?

Plasma membrane, cytosol (semifluid substance), chromosomes (which carry genes), and ribosomes (which make proteins).

Where is the DNA located in a prokaryotic cell?

In an unbound region called the nucleoid.

Why is the surface area to volume ratio critical for cell size limits?

As a cell increases in size, its volume grows proportionately faster than its surface area, limiting the rate at which essential materials can cross the plasma membrane to service the cell's volume.

What is the basic molecular structure of the plasma membrane?

A phospholipid bilayer containing embedded proteins and carbohydrate side chains, featuring outer hydrophilic regions and an inner hydrophobic region.

What structure lines the inner nuclear side of the nuclear envelope to maintain nuclear shape?

The nuclear lamina, which is composed of protein fibers.

What specific cellular process takes place within the nucleolus?

The synthesis of ribosomal RNA (rRNA).

What are the two locations in a eukaryotic cell where ribosomes build proteins?

In the cytosol (free ribosomes) and on the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes).

What are the three main functions of the smooth endoplasmic reticulum (smooth ER)?

Lipid synthesis, detoxification of drugs and poisons, and storage of calcium ions ($Ca^{2+}$).

What are the key functions of the rough endoplasmic reticulum (rough ER)?

Secreting glycoproteins via bound ribosomes, distributing membrane-bound transport vesicles, and acting as a membrane factory for the cell.

What are the distinct functional roles of the cis and trans faces of the Golgi apparatus?

The cis face is the receiving side that accepts transport vesicles from the ER, while the trans face is the shipping side that dispatches sorted vesicles.

How do phagocytosis and autophagy differ regarding lysosomal digestion?

Phagocytosis involves digesting food particles or foreign materials engulfed from outside the cell, whereas autophagy involves recycling the cell's own damaged organelles and macromolecules.

What are the primary roles of the central vacuole in mature plant cells?

Holding cell sap, acting as the main repository of inorganic ions (including potassium and chloride), and playing a major role in plant cell growth.

What evolutionary process is proposed by the endosymbiont theory for the origin of mitochondria and chloroplasts?

An early eukaryotic ancestor engulfed an oxygen-using nonphotosynthetic prokaryote (which evolved into a mitochondrion), and at least one of these cells subsequently engulfed a photosynthetic prokaryote (which evolved into a chloroplast).

What structural characteristics shared by mitochondria and chloroplasts support the endosymbiont theory?

Envelopment by a double membrane, presence of free ribosomes and circular DNA molecules, and the ability to grow and reproduce somewhat independently within host cells.

How do cristae contribute to mitochondrial function?

Cristae are infoldings of the inner membrane that present a large surface area for enzymes that synthesize ATP.

What are thylakoids, grana, and stroma in a chloroplast?

Thylakoids are internal membranous sacs; a granum is a stack of thylakoids; and stroma is the internal fluid surrounding the thylakoid system.

What chemical reaction occurs inside peroxisomes, and what byproduct is produced?

Peroxisomal enzymes remove hydrogen atoms from various substances and transfer them to oxygen, forming hydrogen peroxide ($H_2O_2$).

What specialized role do glyoxysomes perform in plant seeds?

They convert stored fatty acids into sugars to feed the emerging seedling.

What are the three main types of protein fibers that compose the eukaryotic cytoskeleton, ordered from thickest to thinnest?

Microtubules ($25\,\text{nm}$ diameter), intermediate filaments ($8\text{--}12\,\text{nm}$ diameter), and microfilaments ($7\,\text{nm}$ diameter).

What protein dimers build up microtubules?

Tubulin dimers, each consisting of an $\alpha\text{-tubulin}$ and a $\beta\text{-tubulin}$.

What is the structural arrangement of centrioles within an animal cell centrosome?

A pair of centrioles, each composed of nine triplets of microtubules arranged in a ring.

How do cilia and flagella differ in their beating patterns and cell abundance?

Cilia occur in large numbers on a cell surface and use an alternating power and recovery stroke, whereas flagella are limited to one or a few per cell and generate an undulating wave-like motion.

What internal microtubule arrangement is characteristic of motile cilia and flagella?

A $9 + 2$ arrangement, consisting of nine outer doublets of microtubules in a ring surrounding two single microtubules in the center.

How does the motor protein dynein generate bending movements in cilia and flagella?

Dynein feet walk along adjacent microtubule doublets; because the doublets are held in place, the sliding force causes the entire structure to bend.

Which motor protein interacts with actin microfilaments to drive muscle cell contraction and amoeboid movement?

Myosin.

What is cytoplasmic streaming in plant cells, and what drives it?

A circular flow of cytoplasm within cells that speeds the distribution of materials, driven by actin-protein interactions.

What are the three layers that can compose a plant cell wall?

The primary cell wall (thin and flexible, secreted first), middle lamella (thin pectin-rich layer between primary walls), and secondary cell wall (added between the plasma membrane and primary wall in some mature cells).

What major extracellular glycoproteins make up the extracellular matrix (ECM) of animal cells?

Collagen, proteoglycans, and fibronectin.

What are integrins, and what is their role in animal cells?

Receptor proteins embedded in the plasma membrane that bind ECM proteins (like fibronectin) to transmit signals between the extracellular matrix and the cytoskeleton.

What are plasmodesmata, and what substances can pass through them?

Channels connecting adjacent plant cells that allow water, small solutes, and occasionally proteins and RNA to pass directly from cell to cell.

What are the three common types of cell junctions found in animal epithelial tissues, and what are their functions?

Tight junctions (press membranes together to prevent leakage of extracellular fluid), desmosomes (anchoring junctions that fasten cells into strong sheets), and gap junctions (communicating junctions that provide cytoplasmic channels between cells).