Biology-Cell Structure and Function

(Miller & Levine, Ch. 8.1–8.2)

Plasma (Cell) Membrane

phospholipid bilayer with proteins. Function: regulates what enters and leaves the cell. How: hydrophobic tails block many substances while membrane proteins allow selective transport of needed materials.

Cytoplasm

jelly-like fluid filling the cell. Function: supports organelles and is the site of chemical reactions. How: watery, enzyme-rich fluid allows molecules to move easily and reactions to occur.

Nucleus

large membrane-bound organelle containing DNA. Function: controls cell activities. How: separates DNA from the cytoplasm, allowing controlled gene expression.

Nuclear Envelope

double membrane surrounding the nucleus. Function: protects DNA and regulates interaction with cytoplasm. How: two membranes provide extra protection while nuclear pores control exchange.

Nuclear Pores

protein-lined openings in the nuclear envelope. Function: control movement into and out of the nucleus. How: selective pores allow RNA and ribosomes to pass while blocking other materials.

Chromatin / Chromosomes

DNA wrapped around proteins. Function: stores genetic information. How: loose chromatin allows genes to be read

Nucleolus

dense region inside the nucleus. Function: produces ribosomes. How: concentrated RNA and proteins allow efficient ribosome assembly.

Ribosomes

small structures made of rRNA and proteins. Function: synthesize proteins. How: their shape allows reading mRNA and joining amino acids.

Rough Endoplasmic Reticulum

membrane system with ribosomes attached. Function: modifies and transports proteins. How: ribosomes feed proteins directly into the ER for folding and transport.

Smooth Endoplasmic Reticulum

membrane system without ribosomes. Function: synthesizes lipids and carbohydrates; and detoxifies chemicals. How: open membrane surface holds enzymes for lipid (and carbohydrates) production and detoxification.

Golgi Apparatus

stack of flattened membranes. Function: modifies, sorts, and packages proteins. How: enzymes modify proteins and the layered structure sorts and ships them.

Transport Vesicles

small membrane-bound sacs. Function: transport materials within the cell. How: membrane encloses and protects materials during transport.

Mitochondria

double-membrane organelle. Function: produces ATP (energy). How: folded inner membrane increases surface area for energy reactions.

Lysosomes

enzyme-filled membrane-bound sacs. Function: break down waste and old organelles. How: digestive enzymes work safely inside the enclosed space.

Vacuole

large membrane-bound storage compartment. Function: stores water, nutrients, and waste. How: large size allows storage

Cell Wall (plant cells)

rigid outer layer outside the membrane. Function: supports and protects the cell. How: cellulose fibers give strength and prevent over-expansion. PLANT CELLS ONLY

Chloroplast (plant cells)

green organelle with stacked membranes. Function: performs photosynthesis. How: chlorophyll in thylakoids captures light energy. PLANT CELLS ONLY

Centrioles (animal cells)

paired cylindrical structures made of microtubules. Function: help with cell division. How: organize spindle fibers that separate chromosomes. ANIMAL CELLS ONLY