W7.1_Cell

Question 1

Contrast cell and organelle. Define and state the purpose of cell membrane and cytoplasm. What is cytosol?

Answer 1

• Cell: basic unit of life
• Organelle: small structure in a cell with specific function
• Cell membrane: two layers of phospholipids, proteins integrating into the membrane
• Selectively permeable to regulate materials entering/exiting the cell
• Cytoplasm: made of fluid and organelles except nucleus
• Cytosol: liquid/non-organelles in cell

Question 2

Define and state the purpose of nucleus. What are anucleate cells and nucleoplasm?

Answer 2

• Nucleus: membrane-bound, contains DNA
• Control centre of cell, regulates DNA & RNA actions (cell division, protein production)
• Usually large, spherical, near the centre of cell (can be oval/flattened/lobed too)
• Anucleate cells: without nucleus (ex. RBC to increase oxygen carrying capacity)
• Nucleoplasm: amorphous fluid with soluble proteins, RNA, ribonucleoproteins, small molecules, chromatin

Question 3

Define and state the purpose of nuclear envelope, nucleolus, and DNA. What is the difference between chromatin and chromosome?

Answer 3

• Nuclear envelope: double layer of lipids
• Regulates what enters/exits nucleus (ex. drugs that bind DNA/RNA)
• Nucleolus: inside nucleus, separated from DNA
• Produces RNA to make proteins
• DNA (Deoxyribonucleic acid): locked in nucleus, made of nucleotides
• Give information on how to make proteins
• Chromatin (unorganised at normal state, 50% proteins + 50% DNA)
• Chromosome (organised before cell division)

Question 4

Define and state the purpose of endoplasmic reticulum, ribosomes, vacuoles and vesicles.

Answer 4

• Endoplasmic reticulum: highly convoluted single membrane enclosing tubes and channels
• Transportation route for proteins to Golgi body
• Rough ER: with ribosomes, sheet-like, carry out extensive protein synthesis, near nucleus
• Smooth ER: without ribosomes, tubular, carry out lipid and drug metabolism, far away from nucleus
• Main functions: translocation of proteins, glycosylation of proteins//detoxification of drugs, assembly of lipid bilayers
• Ribosomes: small, circular organelles
• Makes proteins from mRNA/tRNA
• Vacuoles and Vesicles: small, membrane-bound organelle
• Storage for water, nutrients, waste

Question 5

Define and state the purpose of lysosomes. Explain cellular digestion and apoptosis with respective to the action of lysosomes.

Answer 5

• Lysosomes: small, membrane-bound organelles
• Contains packet of enzymes that break down materials in cell (organelles/proteins/phagocytosed bacteria)
• Function: digests macromolecules, cleans up broken down molecules, digest bacteria after WBC’s attack
• Cellular digestion: lysosomes fuse with food vacuoles -> polymers digested into monomers -> pass to cytosol to become nutrients for cell
• ∵ Lysosomal enzymes work best at pH≈5 (won’t function well when leaked into cytosol as they are denatured)
• ∴ Proteins in lysosomal membrane pump H+ ions from cytosol to lysosome
• Used in apoptosis (breaks open and kill cells that are supposed to be destroyed)

Question 6

Define and state the purpose of mitochondria. Explain the process of energy conversion in mitochondria.

Answer 6

• Mitochondria: double membrane-bound, kidney shaped
• Energy conversion (generated from food energy to ATP), cellular aerobic respiration (oxidative phosphorylation)
• Mechanisms: electron transport chain, proton gradients, coupled ATP synthesis
• Large molecules broken down into subunits -> converted to few key molecules -> oxidised to produce ATP (molecular unit of intracellular energy currency that recycles 1k-1.5k times per day)
• Energy from high energy electron pump protons/H+ from matrix to intermembrane space -> protons flow back to matrix through ATP synthase due to electrochemical proton gradient -> drives coupled ATP synthesis

Question 7

Define and state the purpose of Golgi appartus and cytoskeleton.

Answer 7

• Golgi apparatus/body: pancake-shaped, layered organelle, slightly concave, polarised
• Protein modifications (addition of sugars/fatty acids/phosphate groups) to change its shape and function
• Protein processing: cleavage of peptides to produce activated proteins
• Protein sorting and localisation
• Cytoskeleton: microfilaments and microtubules extended across the entire cytoplasm
• Provide supporting framework, give shape/structure to cell
• Actin filaments change the shape of cell
• With associated motor proteins: move/organise organelles/vesicles
• Whole cell movement: polarised and directional, important in development

Question 8

Define and state the purpose of centrioles, cilia and flagella. Define motility.

Answer 8

• Centrioles: microtubules
• Help divide the cell during cell division
• Cilia (amoeba, innering lining of cells) & Flagella (bacteria): many short fibres/1 long fibre
• Provides movement for cell/objects by cell
• Motility: ability to swim