Lecture Notes-14 Biology 1004
North Arkansas College
Topic: Cell Structure and Function (Two Basic Cell Types)
Procaryotes
- Unicellular organisms (bacteria, cyanobacteria).
- No well-defined cell nucleus.
- No internal membranes noted in higher organisms.
- They have a complex cell wall made up of peptidoglycan (2 sugars and peptide).
Eucaryotes
- True nucleus.
- Larger and often multi-cellular (10-100 m m).
- Internal membranes - chloroplast, mitochondria.
- Complex cytoplasm.
- The cytoplasm is compartmentalized (enzymes with specific functions are separated and localized into specific compartments).
Components of Eucaryotic Organisms
- Nucleus
- Size - 5 m m
- Composition - made of DNA - chromosomes.
- May contain RNA (mRNA) and some proteins for ribosomes.
- Cytoplasm - nucleoplasm.
- Bound (surrounded) by 2 membranes.
- Chromatin - long strands of chromosomes (not visible as chromosomes) - become shortened, thickened and then become visible as chromosome.
- Chromosomes made up of genes. Gene - a sequence of DNA that codes for a specific product (usually a protein). Some genes are "turned on" (expressed) and form products, while other genes are ‘"turn off".
- Chromosome exhibits regulation.
- Nuclear lamina - inner nucleus membrane:
- Helps maintain nuclear shape.
- Helps direct substance toward or away from nuclear pores.
Nuclear pores - (~10 h m):
- Allows movement of proteins in and out of nucleus. Pores of the nucleus are often filled (plugged) with substances called vaults that stick in the pore and close it. These vaults do more than act as plugs for the nucleus pore, they trap substances and prevent them from exerting activity (proteins, chemotherapy drugs) and transport to the cellular membrane for elimination.
Nucleolus - chromatin ribosomal subunits (protein, chromatin, RNA).
