Cell Membranes & Protein Synthesis

• Light microscopy allows study of living cells with fewer artifacts than TEM and SEM

Cell Membranes

• Phospholipid bilayers have hydrophobic tails clustered in the interior
• Phosphate heads face the hydrophilic outside and inside of the cell
• Proteins are embedded in and attached to the membrane
• Area is proportional to a linear dimension squared (100 times the surface area with 10')
• Volume is proportional to a linear dimension cubed (1,000 times the volume with 10^3)
• Smaller cells have a greater ratio of surface area to volume
• Narrow, elongated shapes and microvilli increase the surface area relative to the volume of a cell

Protein Synthesis

• Genetic instructions for specific proteins are transcribed from DNA into mRNA
• mRNA passes into the cytoplasm to complex with ribosomes
• There it is translated into the primary structure of proteins
• Ribosomal subunits are synthesized in nucleoli from rRNA (transcribed from DNA) and proteins imported from the cytoplasm

Smooth ER

• Smooth ER in different cells may house enzymes that synthesize lipids (including steroids)
• Smooth ER may also metabolize carbohydrates, detoxify drugs and alcohol
• Smooth ER can store and release calcium ions in muscle cells

Organelles and Their Functions

• Nuclear envelope is a double membrane that encloses the nucleus with pores that regulate passage of materials
• Rough ER-attached ribosomes produce proteins that enter cisternae, secretory proteins, and membranes
• Transport vesicles carry products of ER and Golgi apparatus to various locations
• Golgi apparatus processes products of ER, makes polysaccharides, and packages products in vesicles targeted to specific locations
• Plasma membrane is a selective barrier that regulates passage of materials into and out of the cell
• Lysosomes house hydrolytic enzymes that digest macromolecules
• Mitochondria features an inner membrane, cristae, and matrix in addition to an outer membrane
• Chloroplasts contain inner and outer membranes, stroma, intermembrane space, granum, thylakoid, and thylakoid space
• Peroxisomes incorporate proteins and lipids made in the cytosol, the ER, or the peroxisome itself and increase in number by dividing

Cytoskeleton Components

• Hollow tubes formed from columns of tubulin dimers with a 25-nm diameter
• Hollow tubes provide cell shape and support (compression resistant)
• Hollow tubes act as tracks for moving organelles and chromosomes during cell division, and beating of cilia and flagella
• Actin subunits are two twisted chains with a 7-nm diameter
• Actin subunits facilitate muscle contraction, maintain cell shape, amoeboid movement, and cytoplasmic streaming
• Supercoiled fibrous proteins of the keratin family are 8-12 nm in diameter
• Supercoiled fibrous proteins reinforce cell shape (tension bearing), anchor nucleus, and form nuclear lamina

Plant Cell Structures

• Middle lamella is present between two adjacent plant cells
• Primary and secondary cell walls in plant cells
• Plant cells contain plasma membrane, cytoplasm, and a central vacuole
• Plasmodesmata facilitate orientation of cell movements

Cellular Components and Their Functions

• Nucleus, chromosomes, centrioles, and microtubules are involved in moving chromosomes
• Microfilaments pinch apart cells
• Nucleus contains chromosomes with DNA, mRNA (to ribosomes) for producing enzymes and other proteins
• Ribosomes, rough and smooth ER, Golgi apparatus, and transport vesicles
• Smooth ER including peroxisomes, detoxify substances
• Lysosomes, food vacuoles, and vesicles enclose damaged organelles
• Cytoskeleton components include microtubules, microfilaments, and intermediate filaments, as well as the extracellular matrix
• Cilia and flagella contain microtubules, and microfilaments (actin) are present in muscles and involved in amoeboid movement
• Desmosomes, tight and gap junctions, and ECM are cell junctions

Middle Lamella

• Structural support to glue cells together
• Storage of inorganic ions and growth via cell expansion
• Photosynthesis for the production of sugars
• Starch storage
• Cytoplasmic connections between cells

Endoplasmic Reticulum Types

• Rough endoplasmic reticulum
• Smooth endoplasmic reticulum

Cell Structures

• Chromatin
• Nucleolus
• Nuclear envelope
• Nucleus
• Ribosomes
• Golgi apparatus
• Plasma membrane
• Mitochondrion
• Lysosome
• Cytoskeleton
• Microtubules