plant cells

main parts of the cell wall

• primary cell wall

• secondary cell wall

• middle lamella

primary cell wall

• thin, formed while cell is expanding

• surround the cell membrane and its contents

• 25% cellulose (unbranched bound in long fibers called microfibrils)

• primary cell wall is pliable, but not elastic

cellulose is a long thread of glucose

• put a few of them together and it’s called a microfibril (think of it like a rope)

  • how they are laid across the cell determines its shape

tensile strength

the maximum pulling stress a material can withstand before it breaks or permanently deforms

the tensile strength of a cellulose microfibril is…

stronger than that of steel

additional aspects of the primary cell wall

• cellulose microfibrils are embedded in:

  • cross linking glycans (branching networks between cellulose) (25-50%)

  • pectic substances (10-35%)

  • protein

    • extensins: for cell growth

    • lectins: recognition of foreign molecules

• apoplasts: fluid in the pores of the primary cell wall

secondary cell wall (prevents expansion)

• occurs between primary cell wall and cell membrane

• formed after cells have finished expanding

• structural function (in xylem)

• appear as ring or spirals

• thicker than primary cell wall

• composition:

  • 41-45% cellulose

  • 30% cross linking glycans

  • 22-28% lignin (provides rigidity)

middle lamella

• “cement” between adjacent primary cell walls

• plenteous in unripe fruit

• we extract pectic substances and use them in jams and jellies as a thickening agent

plasmodesmata

specialized pores through the cell wall that provide a cytoplasmic connection (“cytoplasmic bridges”) between adjacent cells

• how cells communicate with each otherw

what is the protoplast?

everything inside the cell wall, the “living” part of the cell

what makes up the protoplast?

• cytosol

• nucleus

• vacuole

• assorted organelles

• ergastic (non-living) substances; “other things that are dissolved in there”

organelles in both plant and animal cells

• plasma or cell membrane

• nucleus

• cytoplasm/cytosol

• mitochondria

• ribosome

• ER

• peroxisomes

• glyoxisomes

• golgi apparatus

• microtubules

• microfilaments

• intermediate filaments

• cilia/ flagella

• cytomembrane system

plasma/ cell membrane

• phospholipid bilayer with proteins

• selectively permeable

• amphipathic (has hydrophilic & phobic regions)

• glycerol backbone

nucleus

• “brain”

• double membrane (two phospholipid bilayers)

• pores

cytoplasm/ cytosol

• cell contents inside the membrane

• gel-like matrix with other structures embedded

mitochondria

• double-membrane bound

• can be tubular or spherical

• reproduce via fission

• inner membrane has larger SA so it’s folded to fit into the outer membrane

• found in all eukaryotic cells

• site of cellular respiration

ribosome

• sight of protein synthesis (translation)

• not “true” organelles- not surrounded by a membrane

• to export a protein, the mRNA and subunits of the ribosome bind together

endoplasmic reticulum

• series of membranous tubes and sacs (cisternae) that run throughout the cell

• rough ER has ribosomes and is laminar

• smooth ER is tubular

peroxisomes

• membrane sac containing enzymes to metabolizing waste products from photosynthesis

  • fats & amino acids

• hydrogen peroxide is a product of metabolism

• catalase breaks down hydrogen peroxide & serves as a marker enzyme

glyoxisomes

• membrane sacs containing enzymes for fat metabolism

• common in seeds

• contains catalase

golgi apparatus

• pancake like stack of membranes

• important in cells that produce materials for export (secretion)

• have polarity

  • cis- imports vesicle from ER

  • trans- exports vesicles

• site of processing & packaging cellular components

• involved in tagging proteins with carbohydrates

microtubules

• hollow tubes made of a mix of alpha & beta tubulin

  • globular proteins

• ~25 nm in diameter

• for support in cytoskeleton

• movement in cilia & flagella

• spindle in cell division

• colchicine- prevents it from just coming apart

• low calcium concentration favors their formation

microfilaments

• protein strands

• involved with the cell cytoskeleton

• main function is support

• 7 nm in diameter

intermediate filaments

• similar to microfilaments

• made of protein in the keratin family

• ~10 nm diameter

cilia / flagella

• for cellular movements

• cilia= many & short

• flagella= few & long

• not particularly common in plants

the cytomembrane system

• made of ER, vesicles, golgi, cell membrane

microbodies

• a general term for any single membrane bound organelle typically derived from the ER that contains catalase and/or hydrogen peroxide producing enzymes

• peroxisomes & glyoxisomes

microsomes

• “biochemical” term for the fraction that is obtained from high speed centrifugation of cell homogenates

• membrane fragments & ribosomes

oleosome

• aka spherosomes

• lipid bodies

• encased by ½ of a cell membrane

• in other words, just a single phospholipid bilayer

plastids

• double membrane-bound organelles in plants

• contain their own DNA & ribosomes

• semi-autonomous

• reproduce by fission

• light → chloroplast

• starch → amyoplast

• tomato ripens → chloroplast to chromoplast

etiolated

a developing plant that developed in the absence of light, plastids are present but the chlorophyll hasn’t developed yet

rubisco

• present in plastids

• the most abundant enzyme on earth

  • major player in making sugar

types of plastids

• proplastids

• chloroplasts

• chromoplasts

• amyloplasts

• leucoplasts

• etioplasts

proplastids

• small

• precursor to the other plastid types

• found in young cell

• actively growing tissues

chloroplasts

• site of photosynthessi

• photosynthetic pigments

  • chlorophyll

  • carotenes

  • xanthophylls

• packed with membranes- thylakoids

• thylakoid stacks- grana

• “liquidy” material- stroma

• 50-200 per cell

• 145 Kbase pairs

chromoplasts

• non-photosynthetic

• colored plastids

• give some fruits and flowers their color

  • via caratonoids

amyloplasts

• colorless

• starch-storing plastids

• carrots, yucca, potato

leucoplasts

• another term for amyloplasts

• means white, void of color, not caratonoids

etioplasts

• plastid whose development into a chloroplast has been arrested

• contain thylakoids (lack of chlorophyl) in a tubular form

why do plant cells have a large central vacuole?

• energetically efficient means to increase surface to volume ration in the dendritic growth from

• water storage

• waste disposal

• pH regulation

• storage of essential ions

• cell enlargement

• facilitates diffusion

• structural support