MCB Textbook Unit 1 Chapter 2--Parts of a Cell

plasma membrane: selectively permeable

  • proteins called receptors detect signals from the environment of the cell

  • transport proteins help some molecules get across membrane

—-Parts of plasma membrane

  • phospholipids—similar to fat molecules, hydrophobic/hydrophilic—make up up to 50% of membrane

  • proteins: stuck in membrane: make up to 50%

  • sterols—type depends on type of cell. Animal cells have cholesterol in membrane

  • carbohydrates: attached to receptors on outside of plasma membrane

  • FLUID MOSAIC MODEL: basically says that membranes are made of several components and these components can move within the membrane

    • phospholipids and proteins move back and forth, making plasma membrane a fluid structure

Cytoplasm: many chemical reactions that make up the metabolism of the cell happen here—including important reactions that build proteins

Ribosomes: made of ribosomal RNA and proteins—-twisted together to make subunits

Free ribosomes: make proteins that function in cytoplasm

Membrane bound ribosomes: make proteins of membrane or leave cell—-attached to membrane

centrifugation: spinning particles extremely fast to weight them—how fast they fly out, basically

  • prokaryotic ribosomes haves 70 s speed (50/30)

  • eukaryotic ribosomes have a 80 s speed (50/40)

nuclear envelope: two phospholipid bilayers, boundary of nucleus—separates contents of nucleus from cytoplasm

nuclear lamina: “scaffold” of protein cables, support nuclear envelope phospholipid bilayers

chromosomes: bundled up DNA for cell replication

chromatin: functioning normal cell, DNA looks like spaghetti in this form

nuclear pores: how molecules pass through nuclear membrane, proteins organize in rings that penetrate through nuclear envelope

small ribosomal subunit: responsible for binding mRNA and decoding genetic information using transfer RNA

large ribosomal subunit: contains peptidyl transferase center, catalyzes formation of peptide bonds between aminos acids

nucleoli: where ribosomal subunits made— cell ships them out of nucleus to cytoplasm, where join together for protein synthesis

  • when started, nucleoli look like large spots within nucleus

RNA molecules + ribosomal subunits and proteins travel through nuclear pores

endomembrane system:

  • endoplasmic reticulum

    • smooth: makes lipids (phospholipids for membranes) may travel to Golgi apparatus

    • rough: studded with ribosomes—ribosomes making proteins with specific destinations come here as protein made, pushed into lumen, center of rough ER, folded and tagged w/carbs

Golgi apparatus:

  • Golgi Apparatus Overview: The Golgi apparatus is composed of a series of flattened membranous sacs known as cisternae, which are layered on top of each other, functioning as a central hub for modifying, sorting, and packaging proteins and lipids that have been synthesized in the endoplasmic reticulum (ER).

  • Cis and Trans Faces: The Golgi has distinct sides:

    • Cis Face: This is the side closest to the nucleus and acts as the receiving side of the Golgi. Here, vesicles from the rough endoplasmic reticulum merge with the Golgi to deliver newly synthesized proteins and lipids.

    • Trans Face: The side farthest from the nucleus, where processed and sorted molecules exit the Golgi in transport vesicles that will deliver them to their final destinations, which could be within the cell or to the extracellular environment.

  • Molecular Reception and Processing: Once molecules enter the Golgi apparatus, they undergo various modifications, which may include glycosylation (addition of sugar molecules), phosphorylation, and other alterations necessary for their function. This is critical for ensuring proteins and lipids are correctly processed for their specific roles within the cell.

  • Constant Change: The structure of the Golgi apparatus is dynamic, constantly changing as it matures and moves the molecules from the cis face to the trans face. This continuous transformation allows the Golgi to efficiently handle large amounts of material that need to be modified and sorted according to the cell's needs.

  • Final Delivery: After processing, the Golgi packages these molecules into vesicles that then bud off from the trans face. These vesicles are then directed toward specific locations, including the plasma membrane for secretion or locations within the cell for various functions. This targeted delivery is essential for maintaining proper cellular function and communication.

peroxisomes: small organelles encircled by single membrane—-break down lipids, like fatty acids

  • depending on which type of cell they are in, peroxisomes may be specialists in breaking down particular molecules

    • glyoxisomes a special kind of peroxisome, help convert stored oils into molecules that plants can easily use for energy

Mitochondria

  • two membranes: outer and inner. Inner membrane is folded back and forth to create more area for energy extraction’ folds are called cristae

  • space between two membranes is called intermembrane space

  • inside of the mitochondrion is the matrix

Thylakoids/grana

  • sacs of membranes inside chloroplasts

  • stroma: fluid like part of the chloroplast

  • inner thylakoid: fluid filled space

Cytoskeleton: network of protein cables

  • cilia and eukaryotic flagella made of cytoskeleton proteins

  • cytoskeleton protein types

    • microfilaments made of actin. Allow muscles cells to contact, pinch animal cells in 2 during cell division, allows amoeba to crawl

    • microtubules: made of tubulin, inside cilia and flagella, move chromosomes during cell division and railroad tracks

    • intermediate filaments: made of various proteins: lamin, strengthens nuclear membrane, keratin, for strengthens skin cells

  • Motor proteins: partner with actin microfilaments and microtubules, move with ATP to walk along the cables by repeatedly binding, changing shape, and releasing—use chemical energy

    • myosin: partner to actin, causes actin microfilament to slide, sliding motion causes muscle contraction.

      • Also attaches to cellular components, like chloroplasts, movement causes components to flow around cell in a process called cytoplasmic streaming

    • dynein: partners with microtubules (cilia and flagella)—when walks, causes microtubules to bend, makes them flick back and forth like whips

    • kinesin: one end of kinesin molecule attaches to vesicles, other along microtubules: movement causes vesicles to slide around like as if on a railroad track

Cilia and flagella

  • cilia found on cells that make up the surfaces of tissues, such as cells in the respiratory and genital tracts of humans, cilia beat to move fluid and materials along the surface

  • microtubules: paired in doublets, 9 + 2 arrangement, where nine pairs of microtubules are arranged outside the outside of the circle, one pair in the center of the circle

Extracellular matrices:

  • provide additional strength to cells and may attach cells to neighboring cells in multicellular organisms—typically, these layers are composed of long carbs/proteins embedded in a sticky matrix

    • extracellular matrix: layer around animal cells, made of long proteins, such as collagen, embedded in polysaccharide gel (complex carbs)

    • ECM supports animal cells and helps bind them together

      • attach themselves to the ECM via proteins called integrins embedded in plasma membrane

        • integrins bind to the actin microfilaments inside the cell and to ECM proteins called fibronectins that are outside the cell

Prokaryotic Cells

  • cell wall: cell wall made of carb/protein complex called peptidoglycan

    • some archaeans have cell walls, some do not—-but either way, do not have peptidoglycan

  • Capsules, pili, and fimbriae

    • many bacteria produce an additional layer called a glycocalyx outside the cell wall. sticky layer is composed of proteins and carbs that help bacterial cells attach to surfaces and to other cells. Also helps bacterial cells avoid capture by certain cells of the human immune system

    • In addition, some bacteria attach to surfaces and to other cells by slender protein threads called pili and fimbriae

    • these things are crucial to the disease causing process through attachment

  • Bacterial flagella: called flagellin

    • attached to wheel like structure in the cell wall of bacterial cells

    • when the wheel rotates, bacterial flagella spin and cause cell to move forward