cells

cells

the functional units of the body

most cells must perform the following

• maintaining its integrity and shape - dependent on plasma membrane and internal contents

• obtain nutrients and form chemical building blocks - harvest energy for survival

• dispose of wastes -avoid accumulation, disrupting ellular activties

some cell can also do cell division

make more cells of the same type

help maintain the tissue by providing new cells

***some cells lose their ability to divide during the development process

plasma membrane

Forms the outer limiting barrier

Separates internal contents of cell from external environment

Cilia, flagellum, microvilli- modified extension of plasma membrane

cytoplasm

Cellular contents between plasma membrane and the nucleus

Includes cytosol, organelles, and inclusions

cytosol

intracellular fluid

• viscous fluid of the cytoplasm

• High water content

  Contains dissolved macromolecules (carbohydrates, lipids & proteins), small molecules (glucose & AAs) and ions

nucleus

contains the genetic material, DNA

• in the chromatin

Typically only one per cell BUT

number and shape per cell depends on the cell type

erythrocytes with no nuclei

skeletal muscle cells with many (multinucleate)

• red blood cells = 0

• skeletal muscle cell = many

enclosed in nuclear envelope

Largest structure in the cell

externally continuous with rough ER

nuclear pores

conains channel like open passageways

• •allow passage in and out of nucleus

  large particles, ions, water soluble molecules

nuclear envelope

• double phospholipid membrane enclosing nucleus

• separates cytoplasm from nuceloplasm

• externally continuous with rough ER

• contains channel-like nuclear pores to let things in

nucleolus

separate (non-membrane bound) organelle

• dark- staining spherical body

• responsible for production of ribosomes

• not present in all cells

  • many in nerve cells → makes many proteins

  • absent in sperm cells → makes no proteins

nucleoplasm

inner fluid in nucleus

membrane bound organelles

• surrounded by a membrane

• BECAUSE of the membrane – the activities of the organelle can proceed in an isolated environment

  • allows processes of organelle to go on WITHOUT disrupting other cellular processes

• differ in shape, membrane, composition, enzymes = dependent on function

  • nucleus

  • endoplasmic reticulum (smooth and rough)

  • golgi apparatus

  • lysosome

  • peroxisomes

  • mitochondria (unique among organelles)

endoplasmic reticulum

Extensive interconnected membrane network

• separates fluid within structure from cytosol with a continuous lumen

• Extends from nuclear envelope to plasma membrane – making up ~1/2 of the membrane within a cell

• synthesis = provides a place for chemical reactions

• transport = moves molecules through lumen from one part of the cell to another, sequestered away from the cytosol

• packaging and storage = packages and stores newly synthesize molecules

• detoxification: SMOOTH ER detoxifies drugs, alcohol, and poison

• structure formation: segments of ER are pinched off to form transport vesicles and peroxisomes

Rough ER

site of synthesis of proteins destined for secretion, incorporation into the plasma membrane, and as enzymes w lysosomes

Protein production by ribosomes happens here – in rough ER

Proteins inserted into membrane as they are synthesized

Original structure of protein changed – as it’s processed (additions and/or subtractions)

  molecular tags – called signal sequences – determine the destination (an “address”)

Transported out in enclosed membrane sacs that pinch off from the ER membrane → termed transport vesicles

shuttle proteins from rough ER lumen to Golgi apparatus

Plentiful in cells producing much protein – such as insulin (protein) -producing cells of the pancreas

Peroxisomes produced here

smooth ER

site of lipid synthesis and carbohydrate metabolism

Continuous with rough ER

Diverse metabolic processes varying by cell

Some functions:

• synthesis, transport, and storage of lipids

carbohydrate metabolism

• detoxification of drugs, alcohols, and poisons

Plentiful in cells of the testes → to produce the steroid hormone testosterone (steroids are lipids)

Plentiful in liver → to detoxify alcohol, when consumed

golgi apparatus

• two faces: cis face (entry and closer to ER) and trans face (exit)

• synthesis: formation of proteoglycans

• processing molecules: modifying and store proteins

• organelle formation: synthesizes digestive enzymes for lysosomes

• vesicle formation: forms secretory vesicles for delivering components of the plasma membrane and releasing content from the cell by exocytosis

Composed of several elongated, flattened saclike membranous structures (~4-5) → termed cisternae

• “Warehouse” of the cell

Exhibits a DISTINCT polarity

Cis-face →closer in proximity to the ER

• receiving region

• Larger diameter

Trans-face → farther from ER

• shipping region

Functions of Golgi

• Modification, packaging, and sorting of proteins

fusion of transport vesicles from ER at cis-face

modification of molecules, e.g., addition of phosphate group

• Transport of material from cis-face to trans-face – moving b/t the cisternae

• Formation of secretory vesicles and lysosomes – at the trans-face

some vesicles becoming part of plasma membrane

others releasing contents outside cell – via exocytosis

Golgi extensive in cells specializing in protein secretion

endomembrane system - secretory pathway

Extensive array of membrane-bound structures → Includes ER, Golgi apparatus, vesicles, lysosomes, peroxisomes

• Also includes plasma membrane and nuclear envelope

Connected directly or through vesicles moving between them

Provides means of transporting substances within cells

***Mitochondria = the only membrane-bound organelles NOT included in the endomembrane system

• rough ER synthesizes proteins thar is released in a transport vesicle

• vesicle from the rough ER moves to the golgi apparatus

• vesicles fuses with Golgi apparatus at the cis face

• proteisn are modified as they move through golgi → adding carbohydrate

• modified proteins are packaged and released with secrtory vesicle from trans face

• secretory vesicles

  • 1. merge with plasma membrane to insert molecules into the plasma membrane =

  • 2. release contents by exocytosis

  • 3. serve as lysosomes

lysosome

• lyso- meaning “dissolution”

• some from soma, meaning “body”

  it’s a small membraneous sac that dissolves substances

• contain digestive enzymes formed by Golgi (ph 5)

Also participate in autophagy and autolysis → digestion of unneeded/unwanted substances

  autophagy – digesting damaged cell components

  autolysis – breaking down cellular components following cellular death

Digest contents of endocytoses vesicles

Clinical View: Lysosomal Storage Diseases

Group of heritable disorders

Characterized by accumulation of incompletely digested molecules within lysosomes

Mutation in genes that code for one of over 40 lysosomal enzymes

E.g., Tay-Sachs disease → lack enzyme needed to break down complex membrane lipids (gangliosides)

Results in accumulation of lipids within nerve cells

Cellular sign = swollen lysosomes – due to lipid accumulation

Outward signs appear as early as 6 months

Nervous system gets brunt of damage

  paralysis, blindness, deafness, followed by death by age four

Lysosomal storage diseases are an extensive group of heritable disorders that are characterized by accumulation of incompletely digested biomolecules within lysosomes. Lysosomal storage diseases occur because of mutations in the genes that code for one of the more than 40 different lysosomal enzymes. Tay-Sachs disease is one example of a lysosomal storage disease. Lysosomes in affected individuals lack an enzyme needed to break down complex membrane lipids (gangliosides). As a result, these complex lipids accumulate within nerve cells.

The cellular signs of Tay-Sachs disease are swollen lysosomes due to accumulation of the lipid. Affected infants appear normal at birth, but begin to show signs of the disease by the age of 6 months. The nervous system bears the brunt of the damage. Paralysis, blindness, and deafness typically develop over a period of 1 or 2 years, followed by death, usually by the age of 4. Unfortunately, there is no treatment or cure for this fatal disease.

Peroxisomes

MOLECULES broken down by peroxisomes include – fatty acids, amino acids, and uric acid

has more than 50 different enzymes – dependent on cell type

Membrane enclaseds sacs smaller than lysosomes

pinched off vesicles form rough ER

Serves in detoxfication →

• Hydrogen peroxide formed when they remove hydrogen from a molecule – hence their name

• H2O2 (hydrogen peroxide) – then broken down into water and oxygen – via the catalase enzyme

Beta-oxidation = removal of two H-C units at a time from the fatty acid chain

  these two units are further broken down into acetyl CoA – to be taken up by the mitochondria (for use in ATP production)

Most abundant in liver → due to detoxification properties

  AND that they also participate in lipid production → important in the production of BILE

Mitochondria

Oblong shaped organelles with a double membrane

• contaisn genes for producing mitochondria proteins

  • on a separate circular strand of DNA

  • engages in aerobic cellular resporiation

  • complete digestion of fuel molecules to synthesize ATP

Cristae = the folds of the inner membrane

These genes come from a unique, circular fragment of DNA within the mitochondria → part of supporting evidence for the hypothesis that early eukaryotic cells endocytosed small, aerobic bacteria – due to the circular DNA

  interestingly, because we only get our organelles from our mother – mitochondrial DNA is something only passed on from mothers

  there are certain genetic disorders that only get passed on thru mitochondrial DNA

Aerobic respiration = most efficient way to get the maximum number of ATP molecules from each molecule of glucose

  ATP = the “cell’s energy currency”

Mitochondrial #’s increase – thru fission – as demands for ATP increase à such as when one exercises on a regular basis (and needs more energy)

ribosomes

non membrane bound organelles

• Contain protein and ribonucleic acid (RNA)

  Arranged into BOTH a large and a small subunit

    Large subunit with E, P, and A sites

  Made within nucleolus and assembled in cytoplasm

  Bound ribosomes = attached to external surface of ER membrane – forming the rough ER

  proteins for plasma membrane, export (exocytosis), or enzymes within lysosomes

• destine to be incorporated into the plasma membrane, exported from the cell or housed within lysosome

  Free ribosomes = suspended within cytosol

  all other proteins within cell synthesized here

proteasome

• located in cytosol and cell nucleus

• degrade cell proteins through ATP dependent pathway

  • damage protein, incorrectly folded protein, proteins no longer needed

Just as with the lysosomes – proteasomes are responsible for DIGESTION of larger molecules into smaller molecules

  protea – means the substance that it will break down is a PROTEIN

  -somes – from soma – meaning body

  it’s a membraneous sac used in protein digestion

• the proteins are broken down into their building blocks → amino acids

Protein marked with ubiquitin tag for disposal

With age may be unable to normally remove proteins

centrosomes/centrioles

Usually in close proximity to nucleus

centrosomes = made of 2 centrioles

centrioles = made of microtubules

Contains pair of perpendicularly oriented, cylindrical centrioles

Surrounded by protein that is amorphous (without a distinct shape)

PRIMARY FUNCTION = organizes microtubules within the cytoskeleton

Best known for function in cell division

forms the mitotic spindle – which facilitates chromosomal movement during that process

cytoskeleton

Plays roles in:

• intracellular support

• organization of organelles

• cell division

• movement of materials

Extends through interior of cell

• Anchors to proteins in plasma membrane

• Formed by a framework of diverse fibrous proteins, which includes

  • microfilaments

  • intermediate filaments,

  • microtubules

microfilaments

Smallest components of the cytoskeleton

• Actin protein monomers form two twisted actin filaments  - think of twisted pearl strands

Form interlacing network on cytoplasmic side of membrane

Functions of microfilaments:

• help maintain cell shape

• form internal support of microvilli

• separate two cells during cytokinesis

• facilitate cytoplasmic streaming

• participate in muscle contraction

intermediate filaments

Intermediate-sized components of the cytoskeleton

More rigid than microfilaments

Support cells structurally and stabilize cell junctions (b/t cells)

Varied protein composition between cells

e.g., keratin – found in cells of the skin, hair, and nails

microtubules

Largest components of the cytoskeleton

Hollow cylinders

Long chains of the globular protein = tubulin

Impermanent structures – elongated or shortened as needed

  accomplished by addition or removal of tubulin monomers, respectively

Function to:

maintain cell shape

organize and move organelles

form components of cilia and flagella

participate in cellular vesicle transport

separate chromosomes during cell division

cilia and flagella

Movement of BOTH based on MT within their core

  movement REQUIRES energy – provided by the splitting of ATP molecules

• protein extneding from the cell surface

• contains both cytoplasm and microtubule proteins

• neclosed in plasma membrane

cilia

usually found on exposed surfaces of specific cells

usually found in large numbers

this beating of the cilia is known as the mucociliary escalator

  it’s what allows you to cough up things that may have gotten into your lung

flagella

similar to cilia in sturcture

longer and usually appear alone

helps propel an entire cell

only example in humans is sperm cell

microvilli

•Microscopic extensions from surface of plasma membrane

•Much smaller than cilia

•More densely packed, lack powered movement

•Supported by microfilaments

•Form extensive plasma membrane surface

•providing increased surface area needed to absorb nutrients

•e.g., in cells of small intestine

Microfilaments – dense bundle of cross-linked actin proteins

Increased surface area – without the different layers of surface area increase in regions such as the small intestine

  we would need to consume 600X more food, in order to get the nutrients we require