BIO 101 Ch.4 (Inside the Cell)

How is SA-volume ratio relevant to the small sizes of cells?

The high surface area to volume ratio allows for…

• adequate space to exchange nutrients and waste

• more membrane space

• —> more efficient diffusion

Light microscope

• Invented in the seventeenth century

• Limited by properties of light

Electron microscope

• Invented in 1930s

• Overcomes limitation by using beam of electrons

Function of microvilli in the small intestine

Increases surface area for absorption of nutrients

Plasma membrane

Marks boundary between outside and inside of a cell

Regulates passage in and out of a cell

Phospholipid bilayer with embedded proteins

• Polar heads (hydrophilic) of phospholipids face into watery

medium

• Nonpolar tails (hydrophobic) face each other

“Fluid mosaic model” describes the structure

Channel proteins

Form tunnels for specific molecules

Transport proteins

Involved in passage of molecules through the membrane, sometimes requiring input of energy

Cell recognition proteins

Enable our body to distinguish between our own cells and the cells of other organisms

Receptor proteins

Allow signal molecules to bind, causing a cellular response

Enzymatic proteins

Directly participate in metabolic reactions

Junction proteins

• form junctions between cells

• cell-to-cell adhesion and communication

What does the cell theory state?

1. All organisms are composed of cells

2. Cells are the basic unit of life

3. All cells come from preexisting cells

What do all cells share?

• a plasma membrane

• cytoplasm

• genetic material

Prokaryotic cells

lack membrane-bound nucleus

Eukaryotic cells

have nucleus that stores genetic material

Bacterial structure

• Cytoplasm surrounded by cell membrane/cell wall (sometimes a capsule which is another protective layer)

• Plasms membrane is the same as eukaryotes

• Cell wall that maintains shape

• DNA — 1 chromosome in the nucleoid region of cytoplasm

• Ribosomes for protein synthesis

• Appendages

Function of flagella in bacteria

Propulsion

Function of fimbriae in bacteria

attachment to surfaces

Function of conjugation pili in bacteria

DNA transfer

Eukaryote kingdoms

• Plants

• Fungi

• Protists

• Animals

Eukaryotic categories of organelles

• Nucleus and ribosomes

• Endomembrane system

• Energy-related

• Cytoskeleton

Chromatin

• Found in nucleus

• diffuse DNA, protein, some RNA

  • Prior to cell division, DNA compacts into chromosomes

Function of mRNA

Carries genetic information from dna in the nucleus to ribosomes in cytoplasm

Nucleolus

region where ribosomal RNA (rRNA) is made

Nuclear envelope

ouble membrane

• Nuclear pores permit passage in and out

Ribosomes

Carry out protein synthesis in the cytoplasm

Found in both prokaryotes and eukaryotes

Composed of two subunits: mix of proteins and rRNA

Receive mRNA as instructions sequence of amino acids in a polypeptide

In eukaryotes:

• Some free in cytoplasm

• Many attached to endoplasmic reticulum

Endomembrane system

• Nuclear envelope

• Membranes of ER

• Golgi apparatus

• Numerous vesicles

Purpose of endomembrane system

• Helps to compartmentalize the cell

• Transport vesicles that carry molecules

Endoplasmic reticulum

Complicated system of membranous channels and saccules

Physically continuous with outer membrane of nuclear envelope

Rough ER

• Studded with ribosomes

• Modifies proteins in lumen

• Forms transport vesicles going to Golgi apparatus

Smooth ER

• Continuous with rough ER

• No ribosomes

• Synthesizes lipids like phospholipids and steroids

• Function depends on cell

• Produces testosterone, detoxifies drugs

Golgi apparatus

Stack of flattened saccules

Transfer station

Receives vesicles from ER

Modifies molecules within the vesicles

Sorts and repackages for new destination

• Some are lysosomes.

Lysosomes

• Vesicles that digest molecules or portions of the cell

• Digestive enzymes

• Tay-Sachs disease - absence of specific lysosomal enzyme, causing toxins to accumulate

Vacuoles

Membranous sacs

Larger than vesicles

Rid a cell of excess water

Digestion

Storage:

• Plant pigments

• Animal adipocytes

Mitochondria

Found in both plants and animals

Usually only visible under an electron microscope

Bounded by double membrane

Break down carbohydrates to produce adenosine triphosphate

(ATP)

Cellular respiration—needs oxygen, produces carbon dioxide.

Inner membrane folds called cristae that increase surface area

Inner membrane encloses matrix

• Mixture of enzymes assisting in carbohydrate breakdown

• Reactions permit ATP synthesis.

Matrix also contains its own DNA and ribosomes.

Chloroplasts

Use solar energy to synthesize carbohydrates through the

process of photosynthesis

Plants and algae

Three-membrane system

Have their own DNA + ribosomes

Three-membrane system of chloroplasts

• Double membrane enclosing stroma

• Thylakoids formed from third membrane.

• Thylakoid membrane contains pigments that capture solar energy

Cytoskeleton

• network of interconnected protein filaments and tubules

• Extends from the nucleus to the plasma membrane

• Only in eukaryotes

• Maintains cell shape

• Motor proteins — allow cell and organelles to move

Myosin

• motor protein

• • Interacts with actin

  • Cells move in amoeboid fashion

  • Muscle contraction

Kinesin and dynein

• Move along microtubules

• Transport vesicles from Golgi apparatus to final destination

Microtubules

• Small, hollow cylinders

• Assembly controlled by centrosome

• Help maintain cell shape and act as track for organelles

and other materials to move

Intermediate filaments

• Intermediate in size

• Ropelike assembly

• Run from nuclear envelope to plasma membrane

Actin filaments

• Two chains of monomers twisted in a helix

• Forms a dense web to support the cell

Centrioles

• Made of nine sets of microtubule triplets

• Two centrioles lie at right angles

• In animal cells; not present in plant cells

Cilia and flagella

Eukaryotes

For movement of the cell or fluids past the cell

Similar construction in both

• 9+2 pattern of microtubules

Cilia shorter and more numerous than flagella

Primary cell walls of plants

• Cellulose fibrils and noncellulose substances

• Wall stretches when cell is growing

Secondary cell walls of some plant cells

• Forms inside primary cell wall

• Woody plants

• Lignin adds strength

Plasmodesmata

• Plant cells connected by numerous channels that pass through cell

walls

• For exchange of water and small solutes between cells

Exterior cell surfaces in animals

No cell wall

Extracellular matrix (ECM)

• Meshwork of fibrous proteins and polysaccharides

• Collagen and elastin—well-known proteins

• Matrix varies—flexible in cartilage, hard in bone

Extracellular matrix

a meshwork of fibrous proteins and polypeptides in close association with the cell that produced them.

• Collagen—resists stretching

• Elastin—provides resilience

Adhesion junctions

• Internal cytoplasmic plaques

joined by intercellular

filaments

• Sturdy but flexible sheet of

cells

Tight junctions

• Impermeable barrier

• Adjacent plasma

membraned joined

Gap junctions

• Allow communication

between two cells

• Adjacent plasma membrane

channels joined

Which microscope used in cytology provides the best resolution?

Transmission electron microscope