Cell Structure + Function

Question 1

What is the central idea of cell theory?

Answer 1

All cells come from pre-existing cells, all living things are made up of cells, and cells are the basic unit of structure and function in organisms.

Question 2

What common features do all cells share?

Answer 2

They use ATP for energy, follow the central dogma (DNA → RNA → Protein), and have similar main organelles arranged in a consistent manner.

Question 3

What is the difference between eukaryotic and prokaryotic cells?

Answer 3

Eukaryotic cells have membrane-bound organelles (including a nucleus) and are larger, whereas prokaryotic cells lack a membrane-bound nucleus and are generally smaller.

Question 4

What is the primary function of the plasma membrane?

Answer 4

It controls which substances enter and leave the cell and acts as a physical barrier between the cytosol and the extracellular environment.

Question 5

What are the main components of the plasma membrane?

Answer 5

A phospholipid bilayer, proteins, glycolipids, glycoproteins, and cholesterol.

Question 6

What are phospholipids, and what is their structure?

Answer 6

Phospholipids consist of a hydrophilic (water-loving) polar head and a hydrophobic (water-hating) tail.

Question 7

What does the Fluid Mosaic Model describe?

Answer 7

It explains that membrane components (lipids and proteins) are free to move laterally, creating a dynamic, mosaic-like arrangement.

Question 8

What types of plasma membrane proteins are there?

Answer 8

Peripheral membrane proteins (associated but not embedded), integral membrane proteins (inserted in the bilayer), and transmembrane proteins (span the entire membrane).

Question 9

What roles do plasma membrane proteins play?

Answer 9

They participate in enzymatic activity, signal transduction, cell-cell recognition, transport of molecules, and attachment to the cytoskeleton and extracellular matrix.

Question 10

What is cytosol?

Answer 10

The fluid portion of the cytoplasm that contains dissolved substances and supports organelles (excluding the nucleus).

Question 11

What components make up the endomembrane system?

Answer 11

The nucleus, endoplasmic reticulum (rough and smooth), Golgi apparatus, lysosomes, and the plasma membrane.

Question 12

What is the main function of the nucleus?

Answer 12

It stores and protects DNA, regulates the transport of molecules via nuclear pores, and houses the nucleolus for ribosome assembly.

Question 13

Describe the structure of the nucleus.

Answer 13

It is enclosed by a double membrane called the nuclear envelope, reinforced by a nuclear lamina, and features nuclear pores and a nucleolus.

Question 14

How is DNA packaged within the nucleus?

Answer 14

DNA, a double helix, wraps around histones to form nucleosomes; nucleosomes coil into chromatin, which condenses into chromosomes during cell division.

Question 15

How many chromosomes are found in a diploid human cell?

Answer 15

There are 46 chromosomes (22 autosomal pairs plus one pair of sex chromosomes).

Question 16

What is a gene?

Answer 16

A segment of DNA that codes for a specific protein or phenotype.

Question 17

What are ribosomes, and what is their function?

Answer 17

Ribosomes are complexes made of rRNA and proteins that synthesize proteins; they exist as free ribosomes in the cytosol or bound to the rough ER.

Question 18

What is the difference between free and bound ribosomes?

Answer 18

Free ribosomes synthesize proteins for use within the cytosol, while bound ribosomes (attached to the rough ER) produce proteins destined for secretion or for use in organelles.

Question 19

Describe the structure of the endoplasmic reticulum (ER).

Answer 19

The ER is a network of membranous tubules; the rough ER has ribosomes on its surface, and the smooth ER lacks ribosomes.

Question 20

What is the function of the rough ER?

Answer 20

It produces non-cytoplasmic proteins (such as secreted and membrane proteins) and packages them into transport vesicles.

Question 21

What is the function of the smooth ER?

Answer 21

It synthesizes lipids (steroids, phospholipids), stores enzymes and proteins, and detoxifies substances.

Question 22

How is the Golgi apparatus structured?

Answer 22

It consists of a series of flattened membranous sacs called cisternae, with a cis face (entry) and a trans face (exit).

Question 23

What role does the Golgi apparatus play in the cell?

Answer 23

It modifies, sorts, and packages proteins and lipids for transport to their destinations, including secretion or lysosomal delivery.

Question 24

What are lysosomes, and what is their primary function?

Answer 24

Lysosomes are vesicles containing digestive enzymes that break down substances, recycle cellular components (autophagy), and digest entire cells if necessary (autolysis).

Question 25

How do lysosomes maintain an acidic environment?

Answer 25

They use membrane proteins to pump H⁺ ions into the lysosome, ensuring optimal conditions for enzyme activity.

Question 26

Describe the structure of mitochondria.

Answer 26

Mitochondria have a double membrane; the inner membrane is folded into cristae, enclosing a matrix that contains enzymes, and they possess their own ribosomes and circular DNA.

Question 27

What is the main function of mitochondria?

Answer 27

They generate ATP through cellular respiration, earning the title “powerhouse of the cell.”

Question 28

What is the role of the cytoskeleton in cells?

Answer 28

It maintains cell shape, provides structural support, organizes organelles, and facilitates intracellular transport and cell movement.

Question 29

What are the three major components of the cytoskeleton?

Answer 29

Microfilaments, intermediate filaments, and microtubules.

Question 30

What are microfilaments composed of, and what is their function?

Answer 30

They are made of actin, are about 7 nm in diameter, and are involved in cell movement, shape, and muscle contraction.

Question 31

What are intermediate filaments, and what role do they play?

Answer 31

Intermediate filaments (such as keratin) provide mechanical support and help maintain cell integrity; they are less dynamic than microfilaments.

Question 32

What are microtubules made of, and what functions do they serve?

Answer 32

Made of alpha and beta tubulin dimers, microtubules (about 25 nm in diameter) are involved in chromosome organization during cell division, vesicle transport, and support of cilia and flagella.

Question 33

How do the different components of the cytoskeleton contribute to cell function?

Answer 33

Microfilaments aid in motility and shape changes, intermediate filaments provide tensile strength and structural support, and microtubules assist in intracellular transport and cell division.

Question 34

What is the central dogma of molecular biology?

Answer 34

It is the process by which genetic information flows from DNA to RNA to protein.

Question 35

How does cholesterol affect the plasma membrane?

Answer 35

Cholesterol modulates membrane fluidity and stability, making the membrane less permeable and more resilient.

Question 36

What role do glycolipids and glycoproteins play in the plasma membrane?

Answer 36

They are involved in cell recognition and communication by acting as molecular signatures on the cell surface.

Question 37

What are nuclear pores, and what is their function?

Answer 37

Nuclear pores are channels in the nuclear envelope that regulate the movement of molecules between the nucleus and cytoplasm.

Question 38

What is the nucleolus, and why is it important?

Answer 38

The nucleolus is a region within the nucleus where ribosomal RNA is produced and ribosome subunits are assembled.

Question 39

How is the rough ER connected to the nucleus?

Answer 39

The nuclear envelope is continuous with the rough ER, allowing direct transfer of materials between these organelles.

Question 40

What is autophagy?

Answer 40

Autophagy is the process by which lysosomes digest and recycle damaged or old organelles.

Question 41

What is the difference between cytosol and cytoplasm?

Answer 41

Cytosol is the fluid component within the cytoplasm that excludes organelles, whereas cytoplasm includes the cytosol plus the organelles (except the nucleus).

Question 42

How do chromatin fibers condense during cell division?

Answer 42

Chromatin fibers condense into loops that further stack together to form chromosomes held together at the centromere.

Question 43

What role does actin play in the function of microfilaments?

Answer 43

Actin provides structural support, enables cell movement, and is key in muscle contraction by forming dynamic filaments.

Question 44

How do the components of the endomembrane system work together?

Answer 44

They collectively package, modify, and transport molecules—proteins and lipids are synthesized in the ER, processed in the Golgi, and distributed via vesicles.

Question 45

Why is a functional cytoskeleton essential for the cell?

Answer 45

It maintains cell shape, enables transport of materials, supports organelle positioning, and facilitates cellular movement.

Question 46

What is the role of the nuclear lamina?

Answer 46

The nuclear lamina provides structural support to the nucleus and helps maintain its shape.

Question 47

How do enzymes in the Golgi apparatus contribute to protein processing?

Answer 47

They modify proteins (e.g., by adding carbohydrate groups) as they pass through the cisternae, ensuring proper folding and functionality.

Question 48

How do mitochondria possess their own genetic material?

Answer 48

Mitochondria contain their own circular DNA and ribosomes, enabling them to produce some of their own proteins independently.