Cells` “The smallest functional unit of life”. Cell theory Cells are the structural and...

Cells`

“The smallest functional unit of life”

Cell theory

• Cells are the structural and functional unit of life

• What an organism does is determined by the activity of its cells

• “…the biochemical activities of cells are dictated by the relative number of their specific subcellular structures”

• Reproductive activities are cell based

p. 62

Components of the membrane

Proteins: as receptor, channel, carrier, marker, anchoring spot to surrounding cells, enzymes (acting inside or outside the cell), anchoring internally for cystoskeleton- about ½ total membrane mass

Some proteins are “integral”- extending through the entire membrane

Other proteins are “peripheral”- inside or outside the cell.-supporting filaments-enzymes

See 64,65

Cell Components

• Plasma membrane

• Cytoplasm

• Nucleus


Lipids: phospholipds, most are “unsaturated”, which because of molecule

shape, makes the membrane more fluid

Cholesterol: helps form membrane; precursor for hormones “some 20% of the lipid…” p. 64

See 65

Glycolipids


Proteins (surface): superficial proteins are “glycoproteins”- sugar+protein forming the “glycocalyx” – a region around the cell surface with many carbohydrates.

The variability of the glycoproteins causes this layer to act as an identifier- specific markers identify specific cells.

This plays a role in immune cell function (recognizing foreign cells) and reproduction (sperm recognizing egg)

See 65


Carbohydrates: joined with proteins as glycoproteins, joined to lipids as glycolipids.- found on the outer layer, can serve as markers for cell recognition

See 65

Junctions with other cells/tissue

• Tight junctions- prevent leakage going between cells

Membrane appendages

“Tight” Not so tight


• Desmosomes- lock cells together where cells are under mechanical stress (skin, heart). Connections are made not just between adjacent cells, but through a cell, distributing stress more broadly

Membrane appendages

See p. 67


• Gap junctions- allow passage of ions and other small molecules (simple sugars) between cells.

• Recall the depolarization of heart cells

Membrane appendages

See p. 70

Transport through the membrane.

CellsTransport through the membrane is selective, and occurs via passive and active processes.

Passive processes

Diffusion:

Facilitated diffusion

Osmosis:

Filtration:

Cells

Passive processes

Diffusion: depends on concentration gradients….

High concentration--> Low concentration

↑ with temperature, smaller particle size

Cells

Diffusion: Driven by kinetic energy of matter

Solute moves from area of high concentration to low concentration

Cells

Diffusion

The route a substance takes through the membrane depends on its size, shape, charge and solubility.

In cells, non-polar and lipid soluble substances can pass through (alcohol, fatty acids, steroids….., CO2, O2) the membrane w/o a channel or gate)

Water soluble substances require a channel in the membraneThese channels may let substances through on the basis

of size or shape

See p. 69

Cells

Passive processes

Facilitated Diffusion: depends on concentration gradients….

High concentration--> Low concentration

Depends on carriers (proteins in the cell membrane) or channels (water filled– allows smaller particles)

CellsPassive processes

Facilitated diffusion: specific carriers exist for certain essential, large, non-lipid soluble substances.

Transportation depends on binding to, being recognized by a receptorA passive process- no ATP required.Ex: glucose See p. 69

CellsPassive processes

Rate of transport dependent on # of carriers, not just concentration, so once carriers are saturated, further increase of concentration has no impact on diffusion rate

See p. 69

Cells

Osmosis: water moves through a semi-permeable membrane to equalize concentrations

Cells

Passive processes

Osmosis

Think of this either of 2 ways:1) there may be a higher concentration of water

on one side of a membrane and it moves towards the other side. (High concentration--> low concentration)

2) water moves to equalize concentrations on either side of a semi permeable membrane. That is, water is drawn to the side where solute is more concentrated.

Think: salting a slug….. Sugaring berries

See p. 70

Cells

Filtration: driven by hydrostatic pressure

• Note that water is able to move through the phospholipid bilayer by osmosis– not just through channels in the membrane

p. 70

New words

• Osmolarity- the total concentration of all solute particles in a solution

• Hypotonic- a solution having lower concentration (compared to cells introduced to the solution)

• Hypertonic- a solution having higher concentration (compared to cells introduced to the solution)

See p. 71

Cells

Active processes: require ATP

See steps on p. 76

Carriers bind to the substance being transported and move it against the substance’s concentration gradient

In primary active transport, the ATP directly powers the particle movement.

In secondary active transport, the particle movement is indirectly powered by ATP

Cells


See steps on p. 76

Primary- analogy: a truck carries water up hill.

Secondary:- a truck carries water up hill, then the water flows back downhill, causing a water wheel to turn.

Cells

Active processes: (example of primary)

Na-K pump: maintains a low intercellular Na level, and high potassium level, inside a cell

See steps on p. 74

Cells


Vesicular transport- a vesicle with walls like the cell’s membrane encloses a substance (large particle or liquid) for transport into or out of a cell.

See steps on p. 78

Cells


See steps on p. 76

Related terms:

Phagocytosis: “cell eating”Pinocytosis: “cell drinking” (“sampling”)Endocytosis: taking into the cellExocytosis: secreting from the cellTranscytosis: moving from one side of the cell to another

• We have seen that the membrane is selectively permeable

• Among the substances selected for are ions, resulting in different ion compositions intracellular compared to extracellular

Cell Membrane: potential

• We have seen that the membrane is selectively permeable

• This selectivity results in the inside of the cell being negative (collected more negatively charged ions) compared to the outside


“Players” in the membrane potential are K+, Na+, Cl- and proteins inside the cell that carry a negative charge.

Also: different ions move through the membrane at

different rates- both actively and passively

AND: these ions move with both concentration

gradients AND electrical gradients


Because there are many different ions involved,

both positive and negative, we will refer to an

“electrochemical” gradient, which includes (for

example) the notion that an paricle might not

reach a concentration equality because there is a

resistance based on a ionic gradient “pushing”

the other way.


Cell adhesion molecules (CAM)

• “anchors” to surrounding cells

• Used by moving cells to grab stationary cells and “pull past” them

• Signal WBCs to an affected area

• Other functions

Cell Membrane: interactions with other cells

Functions:

Contact vs Signal communication

• Cells can communicate by physical contact with each other, as in the case of immune cells “checking out” a target cell

• Cells can communicate via some chemical signal- like a hormone or neurotransmitter- this may involve a “2nd messenger system” in the target cell (p. 81,82)

Cell Membrane: interactions with other cells

Cytoplasm

• The “broth” of the soup or the water of the fish tank…

• The semi-fluid surroundings and support of the organelles of the cell

• Stored sugars, pigment lipids and other substances are included here

» P. 84

OrganellesMitochondria

•Powerhouse of cell, producing ATP aerobically

•More numerous in cells that are active•Cells may have hundreds of mitochondria

•Two membranes•The outer is fairly smooth

•The inner membrane is folded (forming cristae)

OrganellesMitochondria

• A gel matrix fills the mitochondrion. Enzymes in the matrix and on the cristae participate in oxidation of fuel molecules

•Have their own DNA and RNA and replicate based on this genetic material when there is increased demand for energy by the cell.

Organelles

Ribosomes

•Function in protein synthesis

•May be free floating in the cytoplasm or attached to the endoplasmic reticulum (“rough” ER)

•Free floating make proteins for use in the cytosol

•ER bound make proteins for the cell membrane or for export

•May be free or bound, depending on the protein being assembled ( the same ribosome can be either)

Organelles

Endoplasmic reticulum

• A fluid-filled system of tubes/membranes located near and continuous with the membrane around the nucleus

•“Rough” ER packages proteins made with the ribosomes for export.

•Makes membrane parts for the cell

Organelles

Endoplasmic reticulum

•“Smooth” ER make cholesterol and steroid hormones, metabolize fats, participate in drug detox and glycogenolysis

•In striated muscle (cardiac and skeletal) the smooth ER forms the “sarcoplasmic reticulum” that stores calcium ions

Organelles

Golgi Apparatus• another membranous organelle

•“…major function is to modify , concentrate, and package the proteins and lipids made at the rough ER.” (p. 85)

•Transport vesicles from the ER are received by the Golgi Apparatus. Modifications (sugars are added/subtracted, phosphates added) are made, then the proteins are repackaged in one of 3 forms on the far side of the Golgi apparatus form the ER

Organelles

Golgi Apparatus

• the new packages will:

•Be sent to the cell membrane to secrete the proteins

OR

•Be sent to the cell membrane for incorporation into the membrane

OR

•Act as a lysosome inside the cell

• Lysosomes: do clean-up work• old organelles• bacteria, viruses, etc.•Glycogen break down•Unused/modified tissues during fetal development•Cell “self-digestion”•See list on p. 86

Organelles

Lysosome

• Lysosomes: maintain an acidic environment inside, which is where their enzymes work best

•: keep the enzymes contained, while releasing products of breakdown to the cytosol

Organelles

Lysosome

Organelles

Membranous structures (review)(derived from, forming or continuous with the cell membrane)

cell membrane endoplasmic reticulum Golgi apparatus lysosome Secretory vesicles nuclear membrane/envelope mitochondria peroxisomes

(More) Organelles

Peroxisomes

•Like lysosomes, peroxisomes are membranous sacs.

•Unlike lysosomes, peroxisomes bud off from the ER

(More) Organelles

Peroxisomes

•Peroxisomes help with detoxification (alcohol and formaldehyde) but help “extinguish” free radicals, to protect the cell

•“free radicals” are highly reactive molecules– they cause (undesirable) reactions inside the cell, causing damage– like a fire that has escaped the hearth

Cytoskeleton

• 3 types of rods passing through the cytoplasm

• These have no membrane

• Provides support and movement of the cell and organelles

Cytoskeleton

• Microtubules– Largest of 3 rod types

– Provide shape support for the cell

– Provide attachment points and mechanisms for moving organelles (mitochondria, lysosomes) via motor proteins

– Continually being formed/reformed as cell needs change

Cytoskeleton

• Microfilaments– Smallest of 3 rod types, made of actin– Involved in cell shape change and cell

movement– Involved in cell cleavage during replication– Continually being formed/reformed as cell

needs change

Cytoskeleton

• Intermediate filaments– Relatively permanent within the cell– Attached to desmosomes, functions to reinforce

structure of cell

(More) Organelles

Centrosome and Centrioles

The centrosome is an attachment point for microtubules

The centrosome contains the centrioles- pairs of tubes at right angles to each other which (additionally) help move cell components during mitosis (p. 89)

(More) Organelles

Cilia and Flagella

• Cilia move material across the surface of the cell

•In the trachea, shifts mucus up/out of the lungs•In uterine tubes, moves the egg towards the uterus

•Flagella move the cell : only in sperm, in humans

•In both, the structures arise from centrioles

Microvilli- increase surface areaContain actinSpecialized for absorption and secretion

(digestive and urinary tracts)

Cilia- specialized to move material across the cell’s surface

cilia

(a cell) (a cell)

microvilli

Membrane appendages

Organelles

Nucleus

• Stores cell’s genetic material•Directs what proteins are made, when and how much

•Most cells have one.•Some cells have many (skeletal muscle and others)•One cell type (RBCs) have no nucleus

•So has no repair capacity– limited life

Organelles

Nucleus

• Three regions/structures:

•Envelope (membrane)

•Nucleoli

•Chromatin

Organelles

Nucleus

•Regions/structures:

•Envelope (membrane)

•A double membrane, the outer layer of which is continuous with the ER

•Contains pores allowing movement of particles in/out

•Encloses the nucleoplasm- analogous to the cytoplasm of the cell

Organelles

Nucleus


•Nucleoli (1, 2 or more/nucleus)

• Darker regions within the nucleus, having no membrane

•Sites of ribosome assembly

Organelles

Nucleus


•Chromatin•The genetic material of the cell (DNA)

ANDProteins (histones) involved in the packaging of the DNA and regulation of gene expression

•When the cell is preparing to divide, the chromatin forms chromosomes- bundles of the genetic material

Histone: a protein which the DNA is bound toNucleosome: a “clump” of gathered DNA and histones.

The genetic code is contained in the DNA.

The DNA molecule consists of 2 strands, linked together by many paired “nitrogenous bases”

See p. 97

Nitrogenous base pairs

Adenine------ThymineThymine------AdenineGuanine------CytosineCytosine-----GuanineAdenine-----Uracil

The genetic information codes for (among other things) the formation of amino acids. The information for each amino acid is stored as a triplet of nitrogenous bases. (see figure3.36, p. 103). Other triplets give information about how to read the code (as in “start” or “Stop” messages.)

A “gene” consists of all the triplets which code for a specific protein. (bigger proteins require larger genes– longer instructions for assembly)

Protein synthesis

First, gene to be copied needs to be accessible- the strands unravel and separate

then

1. Transcription: making an RNA template of the bases to be copied (the gene)– this happens in the nucleus

2. Translation:- ribosomes act on/with the RNA to construct the new protein--- this happens in the cytosol.

Transcription: mRNA (messenger RNA) is made as a template from which to build the new protein.RNA polymerase finds the “start” codon, then moves along the gene, linking together the “pairing” nucleotides stopping when the “stop” codon is reached.

See 104, 106, 107

The mRNA undergoes some “editing” before leaving the nucleus

(“pre-mRNA” mRNA) p. 103

Involves : mRNA that came from the nucleus

: ribosomes

: tRNA

: amino acids free floating in the cytoplasm

Translation- assemblage of the protein in the cytoplasm

Each tRNA molecule codes for a specific amino acid, so there are 20+ different kinds. tRNA caries the amino acid coded for on the mRNA to the mRNA and ribosome, and links on to the growing protein chain.

Once the protein is completed, the tRNA detaches and the mRNA (eventually) is degraded by enzymes.

The assembly of the protein takes place near the ER, which then “packages” the completed protein for transport elsewhere in the cell or to the Golgi apparatus for transport out of the cell.

Tissues

4 Types of Tissues

EpitheliumConnectiveMuscleNerve

Epithelium

-Named for numbers of layers and cell shape

-Covers surfaces in contact with the “outside”

-Specialized for absorption, secretion, protection, sensation, filtration

-Have an apical surface (the free surface) and a basal surface (where attached to the basement membrane

-Gland tissues are epithelium

Epithelium

-Have an apical surface (the free surface) and a basal surface (where attached to the basement membrane)

-Adjacent cells are connected as sheets by desmosomes and tight junctions

-The basal layer rests on the basement membrane, comprised of the basal lamina and reticular lamina (115)

-Nerves, but no blood vessels

-Generally good regenerative capacity

All epithelium rests on a basement membrane.

The blood carries nutrients as far as the basement membrane.From there, nutrients must diffuse across.

That’s why, in stratified epithelium, the upper layers start dying:“trickle-up” nutrition only serves those at the bottom

The basement membrane is made of protein fibers and helps keep materials/cells in their proper tissue compartments.

Glandular Epithelium

• “Exocrine” when secretions end up on the surface– on the skin or on a surface contiguous with the skin

• “Endocrine” secretions are released to the blood, lymph or interstitial spaces (Not all are epithelium… more later)

Exocrine glands• Includes single cell

and multicell glands

– Single cell are “goblet cells” producing mucin, which released, dissolves in water to make mucus

See 122

Exocrine glands

• Includes single cell and multicell glands

– Multicell glands have ducts and regions secreting to those ducts (acinar cells). There is generally connective tissue supports and blood supplies

See 122

• Pancreas hereSee 123

Secretion:

Three ways for this to happen:

1) merocrine: when the substance being produced by the cell is released by exocytosis (some cytoplasm is lost)

2) holocrine: the cell is filled with the “secretion” bursts, releasing the material, and dies.

3) Apocrine: present in humans?

Connective tissue types

Connective tissue proper Bone Cartilage Blood

LooseDense

SpongyCompact

HyalineFibrocartilageElastic

Several cell types- details later

Embryonic mesenchyme

Connective tissue

Functions:

Support and protection:

Cartilage and bone(blood and lymph)

Transportation:

Blood and lymph

Energy storage:

Fat

Connective tissue (look at 125)

Characteristics:

-made up of ( in differing degrees) cells, matrix of ground substance and fibers

-blood supply varies with the specific tissue-cartilage very poor-bone very rich-others in between

-an “extracellular matrix” lies between cells- contains proteins that connect tissue, hold water- amount varies with the tissue

Connective tissue fibers:

Collagen: most common, strong and flexible

Elastic: containing the creatively named “elastin” protein.These fibers are wavy and have recoil

Reticular: like a lattice- support organ soft tissue and small vessels

Connective tissue

Matrix

-an “extracellular matrix” lies between cells- contains proteins that connect tissue, hold water- amount varies with the tissue

Connective tissue cells

Fibroblasts: produce and maintain fibers and matrix

Chondroblasts: produce cartilage

Osteoblasts- Bone production

Hematopoietic cells- blood cell production

Macrophages: tissue “pac-men”(also WBCs w/ antibodies)

Fat cells:

Mast cells: contain chemical mediators of inflammation

Connective tissue types

Connective tissue proper Bone Cartilage Blood

LooseDense

SpongyCompact

HyalineFibrocartilageElastic

Several cell types- details later

Connective tissue types:

Loose:

Examples: “areolar”, adipose, reticular

Connective tissue (proper)

Dense:

Examples: Dense regular, dense irregular, elastic


Areolar:

Fibers support surrounding tissue

Matrix (ground substance) holds water

White blood cells/Macrophages act defensively

Nutrients stored in fat (adipose)

See p. 126


Adipose: (cells are adipocytes)

-Like areolar connective tissue, plus a predominance of adipocytes

-Acts as padding, shock absorption, insulation and energy reserves

-good blood supply

-white fat vs brown fat

-see p. 127


Reticular:

-see p. 133

Think “lattice”

A framework supporting cells, esp. in the spleen, lymph nodes and marrow


Dense Regular connective tissue

-Made up mostly of collagen, with fibers oriented parallel, in line with the direction of stress

-Think tendon and ligament


Dense Irregular connective tissue

-Similar components to regular, with thicker collagen fibers, oriented ad various angles

-Think dermis, joint capsules, organ capsules


-Fluid connective tissues

Blood and lymph (including RBC, WBC, Platelets


Cartilage (see pages 131,132)

Maintained by chondrocytes

Poor blood supply and innervation

Types: Hyaline

:Elastic

:Fibrocartilage


Cartilage

Types: Hyaline- at joints, supporting respiratory tract, connecting ribs to sternum

- forms the template of bones in the developing fetus

:Elastic- more flexible; at outer ear, epiglottis, auditory tube

:Fibrocartilage- much collagen; tough; found intervertebral disks, symphysis joints


Cartilage

:Elastic- like hyaline, more flexible having many elastic fibers

- at outer ear, epiglottis, auditory tube



Cartilage



Bone: (see p. 133)

2 structural types: spongy and compact

Components include collagen fibers, with a matrix material reinforced by calcium salts for great rigidity

Good blood supply

Nerve

Nerve tissue consists of two main groups: : the neurons which send and receive signals through the body: the neuroglia which are “support” cells for the neurons, providing protection and maintenance for the neurons:. More details on neuroglia later

Muscle

Smooth Cardiac Skeletal

See 140, 141

Muscle- cont

Smooth muscle: forms the wall of hollow organs

: bladder, stomach/intestines, uterus, blood vessels

: is non-striated, involuntary: contracts in response to stretch- meaning for

example- that when the bladder is stretched (full) it contracts to empty

Muscle

Cardiac: found only in the heart: cells have single nucleus: cells may be branched: cells are connected by gap junctions and communicate with each other through these junctions: connections between cells are intercalated disks:cardiac muscle is striated, involuntary

Muscle (cont)

Skeletal::striated, voluntary: what we usually think of as “muscle”-- like the biceps or hamstring group: provides posture, generates heat, provides

movement, control of sphincters (openings of bladder, bowel…)

: multi-nucleate

Membranes

• Cutaneous

• Mucous

• Serous

Membranes

Mucus--line body cavities open to

the “outside”

-moisten tissue, generally adapted for secretion, absorption

-varying amounts of mucus

-protective

Membranes

Serous--line outside of organs: heart, lungs and GI tract

-provide reduced friction around these moving organs

-composed of two layers of a simple squamous epithelium on loose connective tissue layers

-between the layers is serous fluid

Cells` “The smallest functional unit of life”. Cell theory Cells are the structural and...

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