Chapter 3The Cell

Joe Pistack MS/ED

Typical Cell

Cell-structural and functional unit of all living matter.

Cells vary in size, shape, and function.

Cells vary in structure.

Structure and function are closely related.

Different shapes of cells

Cell Membrane

Cell membrane-encases the cell.

Separates the intracellular material from the extracellular material.

Physically holds the cell together.

Chief function- selection of substances allowed to enter and leave the cell.

Cell Membrane

Semipermeable-ability of the cell membrane to choose substances allowed to cross it.

Cell membrane is composed of phospholipids and protein.

Phospholipids are arranged in two layers.

Functions of the protein molecules in the membrane:◦Provide structural support for the membrane.

◦Binding sites for hormones.◦Pokes holes or pores through the lipid membrane. These pores form channels through which water and dissolved substances can flow.

Typical Cell

Inside the Cell

The inside of the cell is divided into two compartments: 1. the nucleus

2. cytoplasm

Nucleus-control center of the cell, controls the workings of the entire cell.

Nucleus contains genetic information and controls all protein synthesis.

Inside the Cell

Nuclear Membrane-double layered membrane that surrounds the nucleus.

Nucleoplasm-substance that fills the nucleus.

Cytoplasm-gel-like substance found inside the cell but outside the nucleus

Composed primarily of water, electrolytes, and nutrients.

Inside the Cell

The cytoplasm contains:

Organelles-small organs with a specific role.

Inclusion bodies-temporary structures that appear and disappear.

Cytoplasmic Organelles

Mitochondria-power plant of the cell.

Tiny slipper-shaped organelles.

Number of mitochondria per cell depends on the metabolic activity of the cell.

(How hard the cell works) eg. Liver, bone

Cytoplasmic Organelles

Mitochondrial membrane:

Consists of 2 layers.Smooth outer layerInner layer contains many folds or cristae.Enzymes associated with ATP are located

along the cristae.Called the “power plant” of the cell

because of production of ATP.

Mitochondria

Inside the Cell

Cytoplasmic Organelles:

Ribosomes-concerned with protein synthesis.

Endoplasmic Riticulum-network of membranes within the cytoplasm, membranes form channels through which substances move.

Inside the Cell

Endoplasmic Riticulum(ER):

2 types:

- Rough endoplasmic riticulum-(RER) - sandpaper-like appearance - concerned with protein synthesis -Smooth endoplasmic riticulum-(SER) -concerned with the synthesis of lipids and steroids

Inside the Cell

Golgi apparatus-series of flatted membraneous sacs.

Proteins synthesized along the RER are transported to the Golgi through channels

formed by the ER.

The Golgi apparatus packages the protein for synthesis.

Inside the Cell

Lysosomes-membranous sacs containing powerful enzymes.

Lysosomes are digestive organelles.

Lysosomal enzymes break down intracellular waste and debris.

“clean house”

Inside the Cell

Cytoskeleton-composed of threadlike structures called microfilaments and microtubules.

Cytoskeleton helps to maintain the shape of the cell and assists the cell in cellular movement.

Centrioles-paired, rod-shaped microtubular structures, play a key role in cellular reproduction.

On the Cell Membrane

Cilia-short, hairlike projections on the outer surface of the cell.

Cilia use wavelike motions to move substances across the surface of the cell.

Eg. Resp. tract-cilia help to move mucous and dust toward the throat, away from the lungs.

On the Cell Membrane

Flagella-(meaning whip)

Whip-like projections, longer, thicker and fewer in number than cilia.

Help to move the cell.

Eg. The tail of the sperm enables the sperm to swim.

Movement Across the Cell Membrane

Passive and Active Transport:

Both are transport mechanisms that assist in the movement of water and dissolved substances across the cell membrane.

Passive transport-requires no additional energy in the form of ATP.

Movement across the Cell Membrane

Passive transport-water and dissolved substances move without additional energy.

Passive Transport Mechanisms:DiffusionFacilitated diffusionOsmosisFiltration

Passive Transport Mechanisms

Diffusion-most common transport mechanism.

Movement of a substance from an area of higher concentration to an area of lower

concentration.

Equilibrium-point at which no further net diffusion occurs.

Transport Mechanisms

Facilitated diffusion-form of diffusion responsible for the transport of many substances.

Substances move from an area of higher concentration to an area of lower concentration but requires a helper molecule.

Transport Mechanisms

Osmosis-diffusion of water through a selectively permeably membrane.

Semipermeable or selectively permeable membrane allows the passage of some substances

while restricting the passage of others.

The strength of the osmotic pull is directly related to the concentration of the solution.

The greater the concentration, the greater the pulling or osmotic pressure.

Transport Mechanisms

Edema-accumulation of water in the tissue spaces.

Osmotic pressure pulls water into a compartment causing swelling.

Tonicity-ability of a solution to affect the volume and pressure within a cell.

Movement Across a Cell Membrane

Isotonic Solution-”iso=same”.

Same concentration as intracellular fluid.

Movement Across a Cell Membrane

Hypotonic Solution-solution containing no solute.

Movement Across the Cell Membrane

Hypertonic Solution-very concentrated solution, causes cells to shrink or crenate.

Isotonic Solutions

Isotonic Solutions do not cause the cells to swell or shrink.

Most IV solutions are isotonic.

Commonly used isotonic solutions:Normal saline (0.9% NaCl)5% D/W (dextrose or glucose in water)Ringers lactate

Filtration

Filtration-water and dissolved substances cross the membrane in response to differences in pressure. (Pressure pushes the substance across the membrane.)

Active Transport Mechanisms

Active transport-transport mechanism requires an input of energy ATP to achieve its goal.

Endocytosis-intake of food or liquid by the cell membrane.

Particle is too large to move across the cell membrane by diffusion.

Active Transport Pumps

Endocytosos:Particle surrounds the cell membrane,

engulfs it and takes it into the cell.

2 types:

Phagocytosis-the cell eating solid particles.Pinocytosis-ingestion of water droplets, cellular drinking.

Active Transport Mechanisms

Exocytosis-moving of substances out of the cells.

Cell Division

Cell division-necessary for growth and repair.

Some cells reproduce frequently, whereas others do not reproduce at all.

Most cells grow in an orderly manner, cells that grow abnormally may be tumors which may be benign or malignant.

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Cell Division

Rate of cell division depends on type of tissue:Some cells don’t divide but are replaced at

incredible rates:◦ Cells of digestive tract replace every few days ◦ Red blood cells-2 million per second ◦ Nerve cells-not at all

Two types of cell division-Mitosis and MeiosisMitosis

Mitosis is involved with bodily growth and repairMother cell splits into two identical “Daughter Cells”

Meiosis◦ Special type of cell division only found in sex cells

Cell Cycle

Cell Cycle has two major partsInterphase

◦Cell carries on normal functions◦Prepares for mitosis through growth and DNA

replicationMitosis

◦The splitting of a cell into two cells with exactly the same genetic information

◦Divided into four phases Prophase Metaphase Anaphase Telophase

Mitosis

Prophase◦ Chromosomes coil tightly and are composed of two identical

strands of DNAMetaphase

◦ DNA align in a narrow central zoneAnaphase

◦ DNA split into pairs and move to opposite ends of the cellTelophase

◦ Cell wall pinches together forming the daughter cells and both cells enter interphase

Stem Cells

Stem cells are cells that have not differentiatedCells differentiate due to the addition of different

enzymesSometimes cells reproduce in an uncontrolled

and disorganized way and form tumors - there are two types:◦Benign-noncancerous◦Malignant-cancerous

Metastasis is when cancer cells spread. A widespread invasion of cancer can cause death