Cell Structure & Function (College Board AP® Biology): Study Guide

Cell structure & function

• Organelles interact with each other to support cellular function

• Many of the cell's organelles are optimized for efficient metabolism

• This means that the cell can capture, store, and utilize energy to the best effect

• It is a common feature of all organisms, although eukaryotes utilize organelles for this purpose

Eukaryotic cells diagram

Endoplasmic reticulum

• The endoplasmic reticulum (ER) plays an important role in protein synthesis

  • Using ribosomes bound in the membrane of the rough ER

• They provide some mechanical support to the cell

  • Whilst the cytoskeleton performs the bulk of this role, the ER also plays a supporting role 

  • Being made of membrane material (largely phospholipid bilayers), the ER can provide a measure of structural support to the cell

    • Acting as an ultrastructural skeleton

• The ER also plays a role in intracellular transport by

  • transporting proteins out of the ER in vesicles

  • transporting lipids and ions throughout the cell

  • helping vesicles move through the cell

Mitochondria

• Mitochondria play a central role in metabolic reactions

• They are the site of many of the key stages of respiration pathways

• The most metabolically active cells eg, muscle cells tend to have more mitochondria than less active ones e.g., bone cells

Mitochondrial adaptations for metabolism

• The mitochondrial double membrane compartmentalizes the organelle for different metabolic reactions

• Folding of the inner membrane into cristae increases the surface area

  • This allows for more ATP to be synthesized

• The Krebs cycle (citric acid cycle) reactions occur in the matrix (central space) of the mitochondria

• The reactions of electron transport and ATP synthesis take place on the inner mitochondrial membrane

Lysosomes

• Lysosomes contain hydrolytic enzymes, which perform the following metabolic reactions

  • intracellular digestion e.g. of waste organic matter

  • the recycling of a cell's organic materials e.g. excess proteins being hydrolyzed back to amino acids for reuse in the cell

  • programmed cell death (apoptosis)

Vacuoles

• Vacuoles have many roles including the storage and release of

  • macromolecules

  • cellular waste products

• In plants, the vacuole aids in the retention of water for turgor pressure

Chloroplasts

• The chloroplast plays a central role in harnessing light energy in photosynthesis

• And converting it into stored chemical energy in the form of food 

• Within the chloroplast are thylakoids and the stroma

  • The thylakoids are organized in stacks, called grana

    • The light-dependent reactions of photosynthesis occur in the grana

  • Membranes contain chlorophyll pigments and electron transport proteins that make up the photosystems

  • The stroma is the fluid within the inner chloroplast membrane and outside of the thylakoid

    • The carbon fixation (Calvin-Benson cycle) reactions of photosynthesis occur in the stroma