PRX330 Cell Introduction

protoplasm

two distinct regions: cytoplasm & karyoplasm/nucleoplasm

water: 70-85%

proteins: 10-20%

lipids: 2-3%

nucleus

contains nuclear envelope, nucleolus, and chromatin

nuclear envelope

double membrane enclosing the nucleus, decorated with pores that allow substances to flow in and out of the nucleus, continuous with the ER

nucleolus

non-membranous structure, synthesizes ribosomal RNA (rRNA) and assembles ribosomal subunits

chromatin

packages long DNA molecules into more compact, denser structures, material consisting of DNA and proteins

ribosomes

complexes that make proteins; free or bound to rough ER or the nuclear envelope

golgi apparatus

organelle active in synthesis, modification, sorting and secretion of cell products, packages large proteins into secretory granules or vesicles

produce large carbohydrate molecules that combine with proteins produced in the rough ER to form glycoproteins

lysosome

digestive system of the cell

contain hydrolytic enzymes that can break down excess and worn-out cell parts

all of these enzymes are acid hydrolyses which means they require an acidic environment

break down phagocytosed material by either heterophagy or autophagy

endoplasmic reticulum (ER)

responsible for the synthesis and transport of the protein and lipid components of most of the cell’s organelles

communicates with the Golgi appartus and interacts with other organelles, lysosomes and peroxisomes

primary lysosomes

membrane bound intracellular organelles that contain a variety of hydrolytic enzymes that have not yet entered the digestive process

heterophagy

digestion of an external substance phagocytose from the cell’s external environment

peroxisomes

membrane-bound organelles that contain several oxidative enzymes such as catalase and urate oxidase

play an important role in the synthesis of specialized phospholipids necessary for nerve cell myelination

detoxify compounds and break down fatty acids

major sites of oxygen utilization

usually contain enzymes that use oxygen to remove hydrogen atoms from specific substrates in an oxidative reaction that produce hydrogen peroxide (H2O2)

should hydrogen peroxide ever leave the peroxisomes?

no!

catalase

antioxidant enzyme, uses H2O2 to oxidize a variety of other substrates—phenols, formic acid, formaldehyde, and alcohol

proteasomes

small organelles composed of protein complexes that are thought to be present in both the cytoplasm and the nucleus

recognizes misformed and misfolded proteins that have been targeted for degradation

what are the three major cellular mechanisms involved in the breakdown of proteins (proteolysis)?

lysosomal proteolysis: uptake of lysosomes that contain proteases

ubiquitin-proteasome system (UPS): targets proteins for degradation by labeling them with chains of ubiquitin molecules..similar to capture the flag,,if the person takes your flag you have to chase after them before you lose.

mitochondria

the cell’s “power plants”, extracts energy from organic compounds through oxygen-dependent cellular respiration and storing it in ATP

have two membranes: relatively permeable outer membrane and an inner membrane that contains enzymes and transport proteins needed for ATP synthesis

what do mitochondria and nuclei share?

they have their own DNA—> allows them to self-replicate and produce some of their own proteins

mtDNA

mitochondrial DNA, circular double-stranded , inherited from your mother

according to the endosymbiont theory, what were the origins of mitochondria and chloroplasts?

mitochondria: oxygen-using nonphotosynthetic prokaryotes taken into host cells

chloroplasts: photosynthetic prokaryotes

cytoskeleton

network of protein filaments— actin filaments, microtubules, and intermediate filaments

give eukaryotic cells their shape, internal organization, and the ability to move

transports substances within the cell and respond to mechanical forces through mechanotransduction (physical signals —> biochemical responses)

what forms tissues and organs?

cell-to-cell adhesions

extracellular matrix

intricate meshwork of interstitial fibrous proteins embedded in a watery, gel-like substance composed of complex carbohydrates

behaves like glue, but it provides a pathway for diffusion of nutrients and other water-soluble substances between the blood and tissue cells

specialized type: basement membrane/basal lamina

functions of ECM

1. mechanical support

2. control of cell proliferation

3. formation of a scaffold for tissue regeneration

4. establishment of tissue microenvironment

collagen

forms cable-like fibers or sheets that provide tensile strength or resistance to longitudinal stress

elastin

a rubber-like protein fiber most abundant in tissues that must be capable of stretching and recoiling, such as the lungs

fibronectin

a large glycoprotein, promotes cell adhesion and cell anchorage.

tight junctions

holds cells together with a tight seal

adherent junctions, desmosomes, hemidesmosomes

provide strong mechanical adjustments

gap junctions

clusters of communicating tunnels that allow small ions and molecules to pass directly from the inside of one cell to the inside of another

tight junctions

barriers to diffusion, prevent the movement of substances through transport proteins in the plasma membrane, and prevent the leakage of small molecules between the plasma membrane and adjacent cells

desmosomes

brings cells together by forming continuous bands or belts of epithelial sheets or by developing button-like points of contact

act as a system of braces to maintain structural stability

connexons

hemichannels that extend outward from each of the adjacent plasma membranes