Cell Organelles flashcards

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1. 1What does the nucleus do?Tap to reveal

   AnswerIt stores the cell's DNA as chromatin and is the site of DNA replication and transcription. It is enclosed by a double-membrane nuclear envelope perforated by nuclear pores that control what enters and leaves.
2. 2What is the nucleolus and what happens there?Tap to reveal

   AnswerA dense region inside the nucleus, without its own membrane, where ribosomal RNA is transcribed and ribosomal subunits are assembled before being exported to the cytoplasm.
3. 3What are ribosomes made of and what do they do?Tap to reveal

   AnswerThey are built from ribosomal RNA and proteins, and they are the site of translation, where messenger RNA is read to build polypeptides. They are not membrane-bound, so they are not an exception to the rule that prokaryotes lack membrane-bound organelles — every cell has ribosomes.
4. 4How do eukaryotic and prokaryotic ribosomes differ?Tap to reveal

   AnswerEukaryotic cytosolic ribosomes are 80S, built from 60S and 40S subunits. Prokaryotic ribosomes are 70S, built from 50S and 30S subunits — the difference many antibiotics exploit.
5. 5What does the rough endoplasmic reticulum do?Tap to reveal

   AnswerStudded with ribosomes on its cytosolic face, it synthesizes and folds proteins destined for secretion, for the plasma membrane or for lysosomes, and begins adding carbohydrate groups.
6. 6What does the smooth endoplasmic reticulum do?Tap to reveal

   AnswerIt synthesizes lipids and steroid hormones, detoxifies drugs and other compounds, and stores calcium ions. It has no ribosomes on its surface.
7. 7What does the Golgi apparatus do?Tap to reveal

   AnswerIt receives proteins and lipids from the ER at its cis face, then modifies, sorts and packages them into vesicles that leave from its trans face for their final destinations.
8. 8What is a lysosome?Tap to reveal

   AnswerA membrane-bound vesicle containing acid hydrolase enzymes that work best at low pH. It digests macromolecules, engulfed material and worn-out organelles, the last process being autophagy.
9. 9What does a peroxisome do?Tap to reveal

   AnswerIt breaks down fatty acids by beta-oxidation and detoxifies various compounds, generating hydrogen peroxide as it does so. Its enzyme catalase then converts that hydrogen peroxide into water and oxygen.
10. 10What is the structure and function of a mitochondrion?Tap to reveal

    AnswerIt has an outer membrane and a folded inner membrane whose folds are called cristae. The citric acid cycle runs in the matrix and oxidative phosphorylation occurs at the inner membrane, generating most of the cell's ATP.
11. 11What is the structure and function of a chloroplast?Tap to reveal

    AnswerFound in plants and algae, it has a double membrane plus internal thylakoid membranes stacked into grana. The light-dependent reactions occur in the thylakoid membranes and the Calvin cycle occurs in the surrounding stroma.
12. 12Why do mitochondria and chloroplasts have their own DNA and ribosomes?Tap to reveal

    AnswerThe endosymbiotic theory holds that both descend from free-living prokaryotes taken up by an ancestral eukaryotic cell. They retain circular DNA, 70S ribosomes and a double membrane, and divide independently of the cell.
13. 13What does the large central vacuole do in a plant cell?Tap to reveal

    AnswerIt stores water, ions and waste products, and the pressure it exerts against the cell wall creates turgor pressure, which keeps non-woody plant tissue rigid.
14. 14What are the three components of the eukaryotic cytoskeleton?Tap to reveal

    AnswerMicrofilaments made of actin, intermediate filaments, and microtubules made of tubulin. Together they give the cell shape, anchor organelles and provide tracks for movement inside the cell.
15. 15What is the centrosome and what does it do?Tap to reveal

    AnswerIt is the main microtubule-organizing center of an animal cell and contains a pair of centrioles. It organizes the spindle apparatus that separates chromosomes during cell division.
16. 16How is the plasma membrane structured?Tap to reveal

    AnswerAs a phospholipid bilayer with embedded and attached proteins, cholesterol and carbohydrate chains — the fluid mosaic model. It is selectively permeable, controlling what enters and leaves the cell.
17. 17What are cell walls made of in plants, fungi and bacteria?Tap to reveal

    AnswerCellulose in plants, chitin in fungi and peptidoglycan in bacteria. All three lie outside the plasma membrane and give structural support; animal cells have no cell wall.
18. 18How are eukaryotic cilia and flagella built?Tap to reveal

    AnswerFrom microtubules in a 9+2 arrangement — nine outer doublets surrounding two central singlets — enclosed by the plasma membrane. Bending is driven by dynein motor proteins.
19. 19Which eukaryotic structures are bounded by a double membrane?Tap to reveal

    AnswerThe nucleus, the mitochondrion and the chloroplast. Lysosomes, peroxisomes, vacuoles, the Golgi apparatus and transport vesicles are each bounded by a single membrane.
20. 20Which organelles make up the endomembrane system?Tap to reveal

    AnswerThe nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, transport vesicles and the plasma membrane. Mitochondria and chloroplasts are not part of it.
21. 21What is the difference between cytoplasm and cytosol?Tap to reveal

    AnswerCytoplasm is everything inside the plasma membrane except the nucleus, organelles included. Cytosol is only the fluid portion in which those organelles are suspended.
22. 22Where is a prokaryote's DNA located?Tap to reveal

    AnswerIn the nucleoid, an irregular region of the cytoplasm with no surrounding membrane, holding a single circular chromosome. Many bacteria also carry small extra circular DNA molecules called plasmids.
23. 23Which structures do prokaryotic cells lack?Tap to reveal

    AnswerA membrane-bound nucleus and all membrane-bound organelles, including mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus and lysosomes. They do have ribosomes, a plasma membrane and usually a cell wall.
24. 24Which structures are found in animal cells but not in the cells of most higher plants?Tap to reveal

    AnswerCentrioles, which organize the spindle in animal cells; the cells of most higher plants build spindles without them.
25. 25Which structures do plant cells have that animal cells lack?Tap to reveal

    AnswerA cellulose cell wall, chloroplasts, and a large central vacuole that maintains turgor pressure.

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