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LABSTER REVIEWER CELL STRUCTURE

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CELL THEORY

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All cells consist of cytoplasm contained within a cell membrane (plasma membrane).

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They can differ significantly, with major differences between prokaryotic (bacteria and archaea) and eukaryotic (plants, animals and fungi) cells, in their structure and in the organelles they contain.

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Cells within an organism can differ greatly facilitating all the different physiological functions required for life.

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Scientist often found out that living organisms were composed of small compartments or pores.

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Robert Hooke was the first scientist to name these as cells in 1965 after the small rooms that monks inhabit.

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Two scientists are credited developing a cell theory.

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Matthias Jakob Schleiden was a botanist who found cells in all plants he examined

CELL MEMBRANE 

1839, Theodor Schwann, a physiologist found cells in animal tissues

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Where cells came from was still debated until in 1855, Rudolf Virchow, a pathologist added third tenet to cells.

It surrounds the cytoplasm of the cell which serves to separate and protect the cell from its environment.

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Composed of a double layer of phospholipids making it very flexible.

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It is able to host various proteins and semi or selectively permeable.

3 TENETS OF CELL THEORY: 1. All living organisms are composed of cells 2. Cells are the structural and organizational unit of life. 3. All cells come from pre-existing cells EUKARYOTIC CELLS 

The cell is the basic biological unit of all known living organisms.

CYTOPLASM 

It contains all the material in the cell excluding the cell nucleus.

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Comprised of cytosol, a gel-like substance which is enclosed by the cell membrane, and all organelles.

NUCLEUS

LABSTER REVIEWER CELL STRUCTURE

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One of many organelles found within cells.

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Cells typically contain one nucleus each, although certain specialized cells may contain many (muscle cells such as RBC containing none).

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The nucleus contains most of a cell’s DNA molecules organized as multiple linear DNA molecules known as chromosomes. The nucleus is kept separate from cytoplasm by nuclear envelope, another double layer of phospholipids, although this membrane is punctuated by nuclear pores.

MITOCHONDRIA 

It is the powerhouse of the mammalian cells generating a supply of ATP, for use as a source of chemical energy.

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The no. of a mitochondria present in a cell gives an idea as to how much energy it requires. EX. RBC have none but in the liver it contains thousands.

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 Golgi body is an organelle found in the most cells and is a continuation of the endomembrane system.  It functions to package proteins for dispersal throughout the cell or even outside of the cell via secretory vesicles. LYSOSOMES AND PEROXISOME 

This two is thought to be the recycling centers of the cell.

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Both is rich in enzymes and responsible for breaking down many kinds of biomolecules into their parts later for reuse.

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Peroxisomes can be thought of as hazardous water recycling centers as its major function is to reduce the damaging reactive oxygen species into harmless waste products.

ROUGH ENDOPLASMIC RETICULUM 

It Is studded with proteinproducing ribosomes and is the major source of protein translation in the cell. GENERIC ANIMAL CELL STRUCTURE

GOLGI APPARATUS

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Animal cells differ massively in size, appearance and function but some factors are conserved. All cells are comprised of cytoplasm surrounded by a cell membrane. Most cells also contain a nucleus which has a complete copy on DNA a well as other structure as the energy producing mitochondria and protein producing rough endoplasmic reticulum.

Dr. one: Root tips are areas of high growth for many plants.

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EUKARYOTES (eukaryotic cells) 

It contains more specialized organelles such as endoplasmic reticulum, Golgi, mitochondria and lysosomes.

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The eukaryotic ribosomes are larger. They consist of a 60s large subunit and 40s small subunit which comes together to form 80s complete ribosomes.

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The prokaryotic cells have 70s ribosomes.

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Prokaryotes also contain extrachromosomal DNA called plasmids which eukaryotes don’t

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The DNA of eukaryotes is contained within a nucleus whereas prokaryotic DNA is found freely in the cytoplasm in a region called nucleoid.

PROKARYOTES (prokaryotic cells) 

It includes the single cells organism bacteria and archaea.

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Animal cells, plant cells, protist and fungi are eukaryotes.

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Viruses are not included because they are not independently living organisms but are dependent on living cells as host in order to replicate.

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All living share five components: Plasma membrane, cytoplasm, DNA, ribosomes and a cytoskeleton.

CELL WALL 

A cell wall surrounds plant, fungi, bacteria, algae and archaea cells.

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It is a strong structure located just outside cell membrane.

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Plant cell walls are mainly composed of cellulose while fungi cells walls are composed of chitin.

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Glucans, protein and bacterial cells walls are composed of

LABSTER REVIEWER CELL STRUCTURE

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peptidoglycan.

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All cell walls give the cell rigidity and strength, offering protection against mechanical stress and limit the entry of large molecules that may be toxic to the cell.

Neurons are specialized cells responsible for signal transduction in our body.

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Glia is support cells that support and insulate neurons.

TYPES OF ANIMAL CELLS 

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Cells of an animal all contain the same DNA, however they have specialized throughout a process of differentiation to become unique.

Animal cells can be divided into 4 main tissues:

EPITHELIAL TISSUE 

It lines the outer surfaces of organs and blood vessels as well as the inner surfaces of lumens.

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They maintain a strong barrier between diff. types of environments.

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There are three main shapes of epithelial cells: squamous(flat) columnar (tall) and cuboidal (square)

MUSCLE TISSUES: 

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Muscle are unique cells in our body because of their ability to contract which changes both the length and shape of cell. A group of muscles cells contracting together can produce a large force and movement in the body.

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The three types of muscle: skeletal, cardiac and smooth muscle.

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Both skeletal and cardiac contains sarcomere which give the muscle striated appearance.

NERVOUS TISSUES: 

Two main type of cell in nervous system are neurons and glia.

CONNECTIVE TISSUE 

Composed mainly of secreted proteins and it is found between other type of tissue.

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Adipose (flat), bones and blood are some examples

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It is also called as extracellular matrix and composed of 2 types large biomolecules: proteoglycans and fibrous proteins such as collagen. Laminin, fibronectin, and elastin.

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The Extracellular matrix helps regulate a number of cellular functions including adhesion, migration, proliferation, and differentiation.

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The ECM proteins are secreted by cells and the composition of the matrix determines the function of the connective tissue. In muscular and nervous system, there are specific layers of connective tissue that surround muscles and nerves. Epithelial cells often sit on the top of a basement membrane composed of connective tissue that helps differentiate the apical and basal side of epithelium.

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Dr. One: Great work of making an osteocyte! The long cellular processes are called canaliculi and they exchange nutrients between osteocytes. Osteocytes secrete proteins that form a mesh called an extracellular matrix and surrounds the cells.

NEURONS 

Cells that are specialized in transmitting electrical nerve impulses to enable internal communication.

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Neurons are highly variable in size and shape in accordance with what purpose they serve.

Dr. one: The membranous endoplasmic reticulum is continuous with the nuclear membrane.

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Some sections have many ribosomes attached and are particularly important for protein synthesis as well as the folding, modification and transport of proteins.

The cell body or soma serves as the control center where organelles and nucleus are located.

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From the soma, protoplasmic extensions or dendrites extend and connect to neighboring neurons to act as the receiving end.

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The axon arises from the soma and propagates a nerve signal to the synapses

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Neurons are provided by glial cells that provide nutrients, remove debris, insulate the electrical impulses and provide

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It also provides specific microenvironment for the type of tissue that helps maintain its function such as stem cell niche.

CYTOSKELETON 

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It is a network of filamentous proteins that extend from the cell’s nucleus to the cell membrane. It is composed to a variety of proteins including actin and tubulin.

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structure support. 

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It can classify neurons in two ways; Structural and functional

Transmit info from sensory organs in the skin, joints, eyes, ears nose and tounge.and relays it to the CNS

MULTIPOLAR 

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Has a single axon and multiple dendrites extending from the cell body. Most interneuron in the CNS are multipolar neurons EX. Somatic motoneurons. Several dendrites and one axon and most common type is in dendrites and SC

INTEGRAL NEURONS 

Receive, process, store and retrieve info in the brain.

MOTOR NEURONS 

Carry outgoing signals from the brain and spinal cord to muscle and glands.

BIPOLAR 

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Has two processes (one dendrite and one axon) extending from the cell body. EX. Neurons located in olfactory nerve. One main dendrite and one axon mostly found in retina, inner ear and olfactory.

MUSCLE TISSUES 

Muscle is one the most abundant tissues in animals and humans.

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It is composed of cells with the ability to contract and provide particular movement to different parts of the body.

UNIPOLAR 

Has one process extending from the cell body. EX. Sensory neurons.

FUNCTIONAL TYPE OF NEURON SENSORY NEURON

The skeletal, smooth, and cardiac muscle tissues perform several important functions in our bodies: Movement

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External movement – Skeletal muscles are attached to bones and stretches over joints to make the skeleton move as they contract. Others allow us to express our emotions through facial expressions. Internal Movement – Smooth and skeletal muscle tissue is responsible for “hidden movement”, including breathing, digestion, circulation of blood, urination and defecation.

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Glycemic control -

Autonomic Nervous System -

Stability -

Skeletal muscles maintain our posture and prevent unwanted movements

Sphincter control -

Sphincters of both skeletal (voluntary) and smooth (involuntary) muscle tissue control our body openings and passage of food and liquids

Muscular thermoregulation -

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In rest, contractions of skeletal muscles produce up to 30% of the body heart. During exercise, the heat production increase to 40x as much. Smooth muscle is found in the wall of the arteries that supply blood to the skin. When these arteries relax, more blood flow to the skin which increases heat loss. When the arteries contract, blood flow to the skin decreases and less heat is lost from the body.

Skeletal muscles stabilize blood sugar levels by absorbing glucose and store it as glycogen. Up to 500g of glycogen can be stored in the skeletal muscles and the glycogen is converted to energy for the muscle cells, when needed.

The part of the nervous system that responsible for the involuntary control of internal organs

The autonomic nervous system controls:   

Smooth muscle (e.g. blood vessels, gut wall, urinary bladder) Cardiac muscle Glands (e.g. sweat glands, salivary glands)

The ANS has two major division  

Sympathetic Parasympathetic

Autonomic nerves release different neurotransmitters to fire an action potentials that will initiate the contraction mechanism. Besides the nervous control, the smooth and cardiac muscles can also contract due to hormones, pacemaker cells, drugs, or mechanical stretching.

Smooth muscle -

Cells do not have striations

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Controlled by the autonomic nervous system which is the one responsible for the involuntary control of organs.

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Divided into two different subgroups according the cellular disposition

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Each cell is an independent unit, innervated by at least one motor neuron each — allows a finer control of movements due to their independent contraction.

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Multiunit smooth muscle is neurogenic — which means that its contraction must be initiated by an autonomic nervous system neuron.

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Found mostly in large blood vessels, large airways to the lung, the muscles of the eye (iris and pupil), the erector pili muscles

Single unit smooth muscle -

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Interconnected by Gap junctions, which are areas of low resistance, allowing the transmission of action potentials among cells for a coordinated contraction. Motor neurons can stimulate more than one cell at the same time, giving a gross control of movement. However, single unit smooth muscle is myogenic. Myogenic means that there is no need for the input of a motor neuron to contract.

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Single unit smooth muscle is commonly called visceral muscle as it is found in the walls of hollow organs in the digestive and urinary tract, as well as in the reproductive system.

Multiunit smooth muscle

Cardiac muscle -

are only found in the heart, where it constitutes the bulk of the heart’s walls.

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Pump blood into the vessels of the circulatory system.

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Striated like skeletal muscle cells Not voluntary

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Intercalated discs contain gap junctions and desmosomes. Desmosomes prevent adjacent cells from separating during contraction. The gap junctions allow ions to pass from cell to cell, transmitting current across the entire heart.

Neuroglia Cardiac muscle cells have -

myofibrils composed of myofilaments arranged in sarcomeres

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T tubules to transmit the impulse from the sarcolemma to the inferior of the cell,

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numerous mitochondria for energy

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intercalated discs that are found at the junction of different cardiac muscle cells.

A photomicrograph of cardiac muscle cells shows the nuclei and intercalated discs. An intercalated disc connects cardiac muscle cells and consists of desmosomes and gap junctions.

Cardiac muscles are rectangular shaped cells connected by regions called intercalated discs.

The supportive cells of the nervous system (glial cells) are approximately 10x as abundant as the neurons. Glial cells support neurons by providing nutrients, protection, removing debris and unwanted microorganisms, insulating electrical impulses and coordinate activity of neurons. Glial cells of the central nervous system include: Oligodendrocytes – large cells from myelin sheets. Ependymal cells – line the fluid-filled cavities of the CNS Microglia - are phagocytic cells that traverse the CNS to remove Astrocytes – the most abundant type of glial cells Astrocytes provide support to the nervous tissue and their extended pedicles (perivascular feet) wrap around capillaries to the form blood-brainbarrier.

Glial cells of the peripheral nervous system include:

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Schwann cells wrap around and myelinate the neurons found in peripheral nerves. -

Schwann cells also play a crucial role in the healing and regeneration of damaged neurons

Satellite cells surround the cell bodies of peripheral neurons, providing insulation and a stable chemical environment.

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