A2.2: Cell Structures

Cell Theory

-Cells are smallest unit of life

-all living organisms are composed of cells

-cells come from pre-existing cells

-Idea of Robert Hooke

4 Universal Structures

Plasma Membrane, Cytoplasm, DNA, Ribosomes

Plasma Membrane

Structure:

-phospholipid bilayer with embedded proteins and cholesterol

Function:

-Semi-permeable barrier that separates internal/external environment

-controls entry/exit of substance

Cytoplasm

Structure:

-gelatinous liquid, mostly H2O

-cytosol = liquid only, cytoplasm = liquid + dissolved enzymes/proteins/other things

Function:

-dissolved enzymes maintain cell's metabolism

-maintains cell shape & protects organelles

DNA

Structure:

-double helix made of nucleotides

Function:

-contains instructions for all cell functions, specifically making proteins

Ribosomes

Structure:

-2 subunits (large and small) made of rRNA and proteins

-no membrane

-two different sizes

Function:

-Protein synthesis

70S vs. 80S

Size classification (s = Svedberg units) of ribosomes

Prokaryotes have 70S, Eukaryotes have 80S (larger)

Free vs Bound Ribosomes

-free ribosomes make proteins to be used in cytosol, typically enzymes (In Cell)

-bound ribosomes make secretory proteins, like hormones

**ribosomes structurally identical and interchangeable**

**every ribosome initially free, then when needs to make secretory protein, becomes bound to ER**

Everything to Annotate in Prokaryote Structure

nucleoid, naked DNA, 70S ribosomes, cytoplasm, plasma membrane, cell wall (thicker), pili/cillia, flagella

*shape is more rod-shaped, length 2x width*

Nucleoid

Area where circular DNA found (called genophore)

Plasmids

extra circular DNA w/ additional info

Prokaryote Ribosome Size

70S

Cytoplasm in prokaryote

internal fluid, contains enzymes

Cytosol

liquid in cytoplasm

Cell Membrane in Prokaryotes

contains mesosomes, infoldings that increase surface area and act as sites for cellular respiration

Cell Wall (prokaryote)

Made of peptidoglycan, protects cell, maintains shape, prevents bursting (prokaryote cell wants to be a bit turgid)

Flagella

long, slender extension used for movement

Cilia/pili

hair-like, sticks to surfaces, used in bacterial conjugation

7 Functions of life

Nutrition, metabolism, growth, response to stimuli, excretion, homeostasis, reproduction

Nutrition

supply food & gasses from environment for energy, growth and repair

Metabolism

Sum of all biochemical rxns in organism (ex. cellular respiration)

Growth

increase size/# cells over time

Response to Stimuli

perception of internal/external stimuli and responding appropriately

Excretion

removal of waste (CO2, urea, feces)

Homeostasis

maintain stable internal conditions

Reproduction

production of offspring and passing on genes

advantages of multicellularity

-longer life spans (death of one cell doesn't kill organism)

-larger in size (can occupy different niches)

-more complex (allows differentiation of cell types

*however, most organisms still single-celled*

Cell Differentiation

-the different development of cells for different functions, occurs early in life

-Gene Expression: genes are "switched on" and transcribed to produce proteins

Housekeeping genes

about 4,000 genes that are active in every cell type (think of a fixed cost)

Location/Form of DNA

DNA exists in chromatin in the nucleus, only in a chromosome during replication

Euchromatin

houses active genes, loosely packed, allows transcription

Heterochromatin

Houses inactive genes, tightly packed, saves space

Nucleus

Structure:

-nuclear envelope is double membraned (2 phospholipid bilayers) with pores

-contains nucleolus region for ribosome synthesis (proteins for ribosomes synthesized outside of nucleus, travel in to join w/ rRNA)

Function:

-stores genetic info as chromatin (DNA + Histones)

Rough Endoplasmic Reticulum (rER)

Structure:

-made of cisternae, flattened membrane sacs

-has 80S ribosomes attached

Function:

-folds/packages secretory proteins (typically hormones)

-vesicles then bud off and go to Golgi

Smooth Endoplasmic Reticulum (sER)

Structure:

-made of branched, tubular membranes

-NO RIBOSOMES

Function:

-makes lipids (phospholipids/hormones), detoxifies drugs, stores calcium ions for muscles

Golgi Apparatus

Structure:

-Consists of cisternae, flattened membrane sacs

-but curved and not as long as in rER

Function:

-receives vesicles from the rER (cis face); modifies and ships most to plasma membrane for secretion (trans face)

*cis face always faces the nucleus*

Lysosomes

Structure:

-membrane sacs filled with hydrolytic enzymes from Golgi

Function:

-digests food, organelles, and sometimes entire cell (apoptosis)

Mitochondria

Structure:

-Double membrane, like nucleus

-outer membrane is smoother, inner contains cristae (infoldings) which increase surface area

-contains matrix (fluid) inside

-also has own DNA and ribosomes, makes own proteins

Function:

-cellular respiration, makes ATP

*plants and animals*

Sap Vacuoles (Vesicles)

single membraned sack filled with fluid, contains dissolved materials

-animal cells have small, temporary vesicles to store food

-some unicellular organisms (paramecium) use contractile vacuoles to expel water

Central Vacuole

-found in plant cells, stores water, pigments, poison, and maintains hydrostatic pressure

Cytoskeleton

either microtubules (largest) or microfilaments (smallest)

Microtubules

Structure:

-made of tubulin protein

Function:

-found in mitotic spindle fibers

-found in cilia/flagella

-moves organelles within cell (ex. vesicles)

Microfilaments

Structure:

-Made of actin protein

Function:

-cytoplasmic streaming (when you circulate cytosol to transport food/enzymes)

-muscle contraction

-helps animal cells maintain shape

Centrosome

Structure:

-contains 2 paired centrioles

-each centriole made of 9 triplet microtubules

-centrosomes only found in animal cells

Function:

-used as spindle fibers in mitosis/meiosis

Chloroplast

Structure:

-double membrane

-contains stacks of thylakoids inside (thylakoid stack called granum)

Function:

-does photosynthesis, makes glucose

-also may contain starch grains

Cell Wall (plant)

Structure:

-rigid outer layer made of cellulose

Function:

-provides support, protection, prevents excess water uptake, lets plant cell remain upright

Things to label in eukaryotic cell microscope images

nucleus, CHR (look for dark area), ribosomes, rER/sER, Golgi, mitochondria, chloroplast, cell wall, plasma membrane, vacuole

Everything to annotate in animal cell drawing

-nucleus, double membrane w/ pores

-mitochondria, double membrane, 1/2 nucleus size

-golgi apparatus w/ vesicles to and from

-ER, interconnected membrane, (sER and rER)

-ribosomes, 80S

-cytosol (NOT CYTOPLASM)

-cell membrane, one line

Everything to annotate in plant cell drawing

nucleus, mitochondria, golgi, rER, sER, ribosomes, cytosol (same as animal cell)

-chloroplast, two membranes, stacks of disks (granum)

-vacuole, large takes up most space; tonoplast (membrane which surrounds vacuole)

-cell membrane, one line

-cell wall, thicker than cell membrane, outside

Differences between Animal/Plant/Fungi Cell

plastids, cell wall, vacuole, centrioles, undulipodia

Plastids differences in eukaryotic cells

-organelle w/ 2 outer membranes and internal sacs

-not in animal/fungi

-in plant cell in chloroplasts and amyloplasts (starch storage)

Cell Wall differences in eukaryotic cells

-not in animal cell

-made of chitin in fungi

-made of cellulose in plant cells

Vacuole differences in eukaryotic cells

-animal cell, small/temporary

-in plant/fungi, large/permanent

Centrioles differences in eukaryotic cells

-in animal cell, constructs microtubule spindles and cilia/flagella

-not in plant/fungi except in swimming male gametes

Undulipodia differences in eukaryotic cells

-cilia/flagella to generate movement

-present in many animal cells, including male gametes

-absent in plant/fungi except in swimming male gamete

Atypical Cell Structures

Red blood cell, skeletal muscles, aseptate fungal hyphae

Red Blood Cell

-no nucleus

-lets cell be smaller/more flexible/carry more O2

-cannot repair itself

-lives 100-120 days

Skeletal Muscles

-cells fuse together and become large an multinucleate (more than one nucleus)

-a muscle fiber (bunch of cells fused together w/ many nuclei) can be as long as 30 cm

Aseptate Fungal Hyphae

-nucleus divides a bunch w/out cell division

-produces very large multinucleate structure

-divide cells after, results in some cells w/out a nucleus and some with multiple

-"aseptate" = w/out nucleus

Magnification Formula

Magnification = size of image/size of specimen

Electron Microscopy

-utilizes wavelengths of electrons focused by electromagnets

-has higher magnification (x1 Million) and good resolution (clear image)

-kills specimen and only in black/white

Freeze Fracture

-produces images of surfaces within cells

-rapidly freeze sample in liquid propane

-use steel blade to fracture sample

-etch - remove ice crystals via vaporization

-coat - pour vapors of platinum/carbon to form replica (like a mold)

Cryogenic Electron Microscopy (Cryo-EM)

-allows researcher on how proteins change form to carry out function

-flash freeze thin layer of protein solution

-place in electron microscope

-take many images, due to random orientation of protein in solution, use algorithms to produce 3D image of proteins

Fluorescent Stains

-sample absorbs light and re-emits it at a longer wavelength

Immunofluorescence

tag different antibodies in immune system w/ fluorescent markers of different colors

Lets you identify specific proteins produced/utilized by the cell

Endosymbiosis Theory

-Eukaryotic cells evolved from prokaryote engulfing other prokaryote via phagocytosis (cell eating)

-instead of digesting, symbiotic relationship develops

-larger prokaryote provides protection, small provides energy

-overtime, prokaryotes lost some of their independence and became organelles

Endosymbiont

a cell that lives within another host cell with mutual benefits

Endosymbiosis Evidence (5)

For mitochondria and chloroplasts:

-own DNA - circular/naked like prokaryotes

-own ribosomes, size 70S

-double membrane, outer may initially have been a vesicle

-reproduces through binary fission-like process

-affected bio antibiotics - suggests bacterial origins