Biology Chapter: The Cell and Organelles

Study Notes

Composed of cytoplasm, cytoskeleton (in eukaryotes), and organelles.
Organelles are classified into three groups: endomembrane system, mitochondria and chloroplasts, ribosomes and nucleus.

Found in all animal cells and some plant cells, containing several hundred dark spherical bodies.
Membrane-bound sacs filled with digestive enzymes, operating optimally at pH 5.
Functions include:
- Intracellular digestion via enzymes such as lipases, carbohydrases, and proteases.
- Recycling old organelles through autophagy.
- Digesting remains of dead cells through autolysis.
Formation process involves the RER assembling enzymes and membranes, followed by chemical refinement in the Golgi apparatus.

Membrane-enclosed fluid-filled sacs, prevalent in plant and fungal cells.
Size can occupy 30% to 90% of cell volume.
Functions include:
- Providing rigidity to plants via hydrostatic pressure.
- Storage of nutrients and chemicals.
- Breaking down complex molecules similarly to lysosomes in animal cells.
Central vacuole enclosed by tonoplast, controlling chemical passage while allowing water to flow freely.

Both play a crucial role in energy production and contain their own DNA and ribosomes.
Endosymbiotic theory suggests they originated from independent bacteria engulfed by larger cells.

Rod-like structures found in large numbers, especially in animal cells; dimensions range from 0.5-1.5µm wide and 3-10µm long.
Double membrane structure: smooth outer membrane and infolded inner membrane (cristae) that partially divides the matrix.
Primary function: ATP production through cellular respiration (Krebs cycle and electron transport chain).
Animal and plant mitochondria differ in cristae shape: tubular in plants, sheet-like in animals.

Large, flat discs averaging 5μm in diameter and 2.3μm thick, with 1 to 50 present per cell.
Have their own DNA, RNA, and ribosomes, often containing starch granules and oil droplets.
Main function: photosynthesis, converting light energy into sugars, facilitated by chlorophyll.
Composed of double membranes, with internal structures (thylakoids) stacked into grana for light reaction site and embedded with photosynthetic pigments.

Largest organelle, approximately 6μm in size, encased in a double membrane punctuated by nuclear pores.
Nuclear membrane limited permeability; nuclear pores allow selective movement of small molecules and ions.
Functions as the cell's control center, regulating gene expression, DNA replication, and ribosome synthesis in the nucleolus.

Spherical granules measuring 20-25nm, comprised of RNA and proteins; consist of two subunits synthesized in the nucleolus.
Eukaryotic ribosomes have a 80S structure (40S + 60S), while prokaryotic ribosomes are 70S (30S + 50S).
Function: protein synthesis based on mRNA genetic information, synthesizing proteins for use within the cell or for export.

Genetic information transcribed from DNA to mRNA in the nucleus.
mRNA exits the nucleus and attaches to ribosomes in the cytoplasm for translation into amino acid sequences, forming proteins.