Cellular Structures and Organelles Flashcards

Comprehensive practice flashcards covering cellular structures, organelles, prokaryotic and eukaryotic differences, and cell fractionation techniques, based on the EJC Biology lecture notes.

What are the three core components of the cell theory?

1. Cells are the smallest unit of life. 2. All cells come from pre-existing cells. 3. Living organisms are composed of cells.

Why are viruses considered to challenge the cell theory?

They are acellular, lack organelles, do not carry out metabolism, cannot reproduce independently of a host, do not grow or undergo developmental changes, and do not respond to stimuli outside a host.

What is the composition of the bacterial cell wall?

It consists of a polymer called peptidoglycan, which is made of long polysaccharide chains cross-linked by short chains of amino acids.

What is the function of the glycocalyx and what two forms can it take?

It protects bacteria from phagocytosis and enables adherence to surfaces; it can take the form of a slime layer (diffused mass) or a capsule (distinct and thicker layer).

What is the mesosome in a prokaryotic cell?

An inward fold of the plasma membrane that is the site of respiration, making it functionally equivalent to the mitochondria.

What are pili and what is their role in bacterial conjugation?

Hollow, hair-like protein structures; the sex pilus draws two bacterial cells together to form a mating bridge for the transfer of genetic material.

Describe the bacterial chromosome and its location.

It is a single circular, double-stranded DNA molecule associated with histone-like proteins, located in a region of the cytoplasm called the nucleoid.

What are the components of a prokaryotic $70S$ ribosome?

A small ($30S$) subunit and a large ($50S$) subunit.

What are the components of a eukaryotic $80S$ ribosome?

A small ($40S$) subunit and a large ($60S$) subunit, both made of ribosomal RNA and ribosomal proteins.

What determines whether a ribosome remains free in the cytosol or becomes bound to the rough ER?

The presence of a signal peptide, which is a stretch of amino acids in the polypeptide being synthesized that is recognized by a signal recognition particle.

What is the structural composition of a centriole?

A pair of cylindrical structures positioned at right angles, each containing nine triplets of microtubules arranged in a ring.

How do euchromatin and heterochromatin differ in structure and function?

Euchromatin is loosely coiled and expressed, while heterochromatin is tightly coiled (more compact), stains more intensely, and is not expressed.

What are the primary functions of the nucleolus?

It is the site of ribosomal RNA ($rRNA$) synthesis and the assembly of ribosomal proteins with $rRNA$ to form ribosomal subunits.

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

Metabolism of carbohydrates, synthesis of lipids (phospholipids, cholesterol, steroid hormones), and detoxification of drugs and ethanol.

Describe the structural components of the Golgi apparatus.

A stack of flattened, membrane-bound sacs called cisternae, with a cis (forming) face and a trans (maturing) face.

What are the three main functions of lysosomes?

1. Digestion of material taken in by endocytosis. 2. Autophagy (breakdown of damaged organelles). 3. Autolysis (self-digestion of a cell).

What is the endosymbiont theory?

The theory that eukaryotic organelles like mitochondria and chloroplasts evolved from free-living prokaryotic cells that were engulfed by a larger host cell.

What evidence supports the endosymbiont theory for mitochondria and chloroplasts?

They both have double membranes, contain their own circular DNA, and possess $70S$ ribosomes.

Describe the internal structure of a mitochondrion.

It has a double membrane; the inner membrane is folded into cristae to increase surface area, and the fluid matrix contains $70S$ ribosomes, circular DNA, and Krebs cycle enzymes.

What is the internal membrane system of a chloroplast called?

It consists of thylakoids, which can be stacked into grana and joined by intergranal lamellae.

Which organelles are included in the endomembrane system?

The nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and the cell surface membrane.

Trace the pathway of a secretory protein from synthesis to secretion.

Synthesized at rough ER $\rightarrow$ packaged into transport vesicles $\rightarrow$ fused with cis face of Golgi $\rightarrow$ modified and sorted in Golgi $\rightarrow$ bud off from trans face in secretory vesicles $\rightarrow$ fusion with cell surface membrane (exocytosis).

What are the two phases of cell fractionation?

1. Homogenisation (breaking cells into fragments). 2. Centrifugation (separating organelles by spinning).

How does density gradient centrifugation isolate organelles?

Organelles migrate through a sucrose gradient until they reach a position where their density equals that of the sucrose solution, forming a distinct band.

What is the difference in flagella microtubule arrangement between protoctists and bacteria?

Protoctists have a $9 + 2$ arrangement, while bacteria have a $9 + 1$ arrangement.