Eukaryotic Cells

Question 1

What does ‘eukaryote’ mean?

Answer 1

‘Eu’ means true, ‘karyon’ means nucleus; eukaryotes have a true membrane-bound nucleus.

Question 2

What domains of life include eukaryotes?

Answer 2

Eukarya – includes animals, plants, fungi, and protists.

Question 3

How do eukaryotes differ from prokaryotes?

Answer 3

Eukaryotes have membrane-bound organelles, including a nucleus; are larger and more complex.

Question 4

What does the nucleus contain?

Answer 4

Chromatin (DNA + histone proteins), nucleoplasm, and nucleolus.

Question 5

What is the role of the nucleolus?

Answer 5

It is the site of rRNA transcription, processing, and ribosome assembly.

Question 6

What is the nuclear envelope?

Answer 6

A double membrane surrounding the nucleus with nuclear pores for transport.

Question 7

What is the first step of DNA compaction?

Answer 7

DNA wraps around 8 histone proteins to form a nucleosome.

Question 8

How many base pairs are wrapped around a nucleosome?

Answer 8

Approximately 200 base pairs.

Question 9

What binds nucleosomes into 30 nm chromatin fibres?

Answer 9

Histone H1.

Question 10

When is DNA fully condensed into chromosomes?

Answer 10

During cell division.

Question 11

What is the function of the rough endoplasmic reticulum?

Answer 11

Protein synthesis, post-translational modification, and phospholipid production.

Question 12

What is the function of the smooth endoplasmic reticulum?

Answer 12

Lipid/steroid synthesis, detoxification, carbohydrate metabolism, and Ca2+ storage.

Question 13

What is the structure of the Golgi apparatus?

Answer 13

Stack of flattened sacs (cisternae) with cis and trans faces.

Question 14

What is the function of the Golgi apparatus?

Answer 14

Protein/lipid modification, sorting, and packaging.

Question 15

What are vesicles?

Answer 15

Small membrane-bound sacs used for storage, transport, and micro-reactions.

Question 16

How are vesicles formed?

Answer 16

By budding off membranes.

Question 17

What is the function of lysosomes?

Answer 17

Break down biomolecules using >50 digestive enzymes; function in phagocytosis, autophagy, and endocytosis.

Question 18

Why is the lysosomal environment acidic?

Answer 18

To activate enzymes and protect the cell in case of leakage.

Question 19

What are peroxisomes?

Answer 19

Organelles that contain oxidative enzymes for detoxification and lipid/amino acid metabolism.

Question 20

Where do peroxisomes originate?

Answer 20

From the ER, but they also self-assemble like mitochondria.

Question 21

What is the main function of mitochondria?

Answer 21

ATP production via oxidative phosphorylation.

Question 22

What is the structure of mitochondria?

Answer 22

Double membrane: outer is permeable; inner is folded into cristae with an internal matrix.

Question 23

What organelles contain circular DNA and 70S ribosomes?

Answer 23

Mitochondria (and chloroplasts).

Question 24

What theory explains mitochondrial origin?

Answer 24

Endosymbiosis theory.

Question 25

What evidence supports the endosymbiosis theory?

Answer 25

Mitochondria have their own DNA, double membranes, bacterial-like ribosomes, and divide by binary fission.

Question 26

What is the cytoskeleton?

Answer 26

A network of protein filaments providing cell shape, support, and movement.

Question 27

What are intermediate filaments?

Answer 27

10 nm rope-like structures for tensile strength and organelle anchoring.

Question 28

What are examples of intermediate filaments?

Answer 28

Keratin, vimentin, neurofilaments, nuclear lamins.

Question 29

What are microtubules made of?

Answer 29

α- and β-tubulin dimers.

Question 30

What are the functions of microtubules?

Answer 30

Maintain cell shape, aid in cell division, and transport cargo with motor proteins.

Question 31

What are motor proteins that move along microtubules?

Answer 31

Kinesins (anterograde) and dyneins (retrograde).

Question 32

What is microtubule polarity?

Answer 32

They have a dynamic (+) end and a stable (–) end.

Question 33

What is treadmilling in microtubules?

Answer 33

Growth at one end and shrinkage at the other.

Question 34

What are actin filaments?

Answer 34

Thin (5–9 nm) filaments made of G-actin forming F-actin.

Question 35

Where are actin filaments concentrated?

Answer 35

In the cell cortex under the plasma membrane.

Question 36

What are the functions of actin?

Answer 36

Cell shape, movement, muscle contraction, vesicle trafficking.

Question 37

What are myosins?

Answer 37

ATP-dependent motor proteins that interact with actin.

Question 38

What are types of myosins and their roles?

Answer 38

Myosin I (membrane dynamics), Myosin II (muscle contraction), Myosin V (vesicle transport).