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1. Plasma membrane - forms the cell’s outer boundary - separates the cell’s internal environment

from the outside environment - is a selective barrier - plays a role in cellular communication

2. Cytoplasm - all the cellular contents between the plasma

membrane and the nucleus - cytosol - the fluid portion, mostly water - organelles - subcellular structures having

characteristic shapes and specific functions

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3. Nucleus - large organelle that contains DNA - contains chromosomes, each of which consists of a single molecule of DNA and associated proteins - a chromosome contains thousands of hereditary units called genes

Flexible yet sturdy barrier The fluid mosaic model - the arrangement of

molecules within the membrane resembles a sea of lipids containing many types of proteins

The lipids act as a barrier to certain substances

The proteins act as “gatekeepers” to certain molecules and ions

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Consists of a lipid bilayer - made up of phospholipids, cholesterol and glycolipids

Integral proteins - extend into or through the lipid bilayer

Transmembrane proteins - most integral proteins, span the entire lipid bilayer

Peripheral proteins - attached to the inner or outer surface of the membrane, do not extend through it

Glycoproteins - membrane proteins with a carbohydrate group attached that protrudes into the extracellular fluid

Glycocalyx - the “sugary coating” surrounding the membrane made up of the carbohydrate portions of the glycolipids and glycoproteins

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Some integral proteins are ion channels Transporters - selectively move substances

through the membrane Receptors - for cellular recognition; a ligand

is a molecule that binds with a receptor Enzymes - catalyze chemical reactions Others act as cell-identity markers

The cell is either permeable or impermeable to certain substances

The lipid bilayer is permeable to oxygen, carbon dioxide, water and steroids, but impermeable to glucose

Transmembrane proteins act as channels and transporters to assist the entrance of certain substances, for example, glucose and ions

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Passive processes - substances move across cell membranes without the input of any energy; use the kinetic energy of individual molecules or ions

Active processes - a cell uses energy, primarily from the breakdown of ATP, to move a substance across the membrane, i.e., against a concentration gradient

Steepness of concentration

gradient Temperature Mass of diffusing

substance Surface area Diffusion distance

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Net movement of water through a selectively permeable membrane from an area of high concentration of water (lower concentration of solutes) to one of lower concentration of water

Water can pass through plasma membrane in 2 ways:

1. through lipid bilayer by simple diffusion 2. through aquaporins, integral membrane

proteins

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Osmosis

Solutes are transported across plasma membranes with the use of energy, from an area of

lower concentration to an area of higher Concentration Sodium-potassium pump

1

3 Na+

K+

gradient

Na+

gradient Na+/K+ ATPase

Extracellular fluid

Cytosol

1

3 Na+ expelled

3 Na+

ADP

P

K+

gradient

Na+

gradient Na+/K+ ATPase

Extracellular fluid

Cytosol ATP

2 1

3 Na+ expelled

3 Na+

ADP P

P

K+

gradient

Na+

gradient Na+/K+ ATPase

Extracellular fluid

Cytosol

2K+

ATP 2 3 1

3 Na+ expelled

3 Na+

ADP P

P

2 K+

imported

K+

gradient

Na+

gradient Na+/K+ ATPase

Extracellular fluid

Cytosol

2K+

ATP 2 3 4

Active Transport

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Vesicle - a small spherical sac formed by budding off from a membrane

Endocytosis - materials move into a cell in a vesicle formed from the plasma membrane

three types: receptor-mediated endocytosis phagocytosis bulk-phase endocytosis (pinocytosis) Exocytosis - vesicles fuse with the plasma membrane,

releasing their contents into the extracellular fluid Transcytosis - a combination of endocytosis and

exocytosis

Receptor

Mediated

Endocytosis

Neutrophil

Phagocytosis

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1. Cytosol - intracellular fluid, surrounds the organelles

- the site of many chemical reactions - energy is usually released by these

reactions - reactions provide the building blocks

for cell maintenance, structure, function and growth

2. Organelles Specialized structures within the cell The cytoskeleton - network of protein

filaments throughout the cytosol -provides structural support for the cell -three types according to increasing

size: microfilaments, intermediate filaments, and microtubules

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Microtubules

Centrosome - located near the nucleus, consists of two centrioles and pericentriolar material

Cilia - short, hair-like projections from the cell surface, move fluids along a cell surface

Flagella - longer than cilia, move an entire cell; only example is the sperm cell’s tail

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Ribosomes - sites of protein synthesis

Endoplasmic reticulum - network of membranes in the shape of flattened sacs or tubules

- Rough ER - connected to the nuclear envelope, a series of flattened sacs, surface is studded with ribosomes, produces various proteins

-Smooth ER - a network of membrane tubules, does not have ribosomes, synthesizes fatty acids and steroids, detoxifies certain drugs

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Golgi complex - consists of 3-20 flattened, membranous sacs called cisternae

- modify, sort, and package proteins for transport to different destinations

- proteins are transported by various vesicles

Lysosomes - vesicles that form from the Golgi complex, contain powerful digestive enzymes

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Peroxisomes - smaller than lysosomes, detoxify several toxic substances such as alcohol, abundant in the liver

Proteasomes - continuously destroy unneeded, damaged, or faulty proteins, found in the cytosol and the nucleus

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Mitochondria - the “powerhouses” of the cell

Generate ATP

More prevalent in physiologically active cells: muscles, liver and kidneys

Inner and outer mitochondrial membranes

Cristae - the series of folds of the inner membrane

Matrix - the large central fluid-filled cavity

Self-replicate during times of increased cellular demand or before cell division

Spherical or oval shaped structure Usually most prominent feature of a cell Nuclear envelope - a double membrane that separates

the nucleus from the cytoplasm Nuclear pores - numerous openings in the nuclear

envelope, control movement of substances between nucleus and cytoplasm

Nucleolus - spherical body that produces ribosomes Genes - are the cell’s hereditary units, control activities

and structure of the cell Chromosomes - long molecules of DNA combined with

protein molecules

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Transcription

Translation

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The cell cycle is a sequence of events in which a body cell duplicates its contents and divides in two

Human somatic cells contain 23 pairs of chromosomes (total = 46)

The two chromosomes that make up each pair are called homologous chromosomes (homologs)

Somatic cells contain two sets of chromosomes and are called diploid cells

Interphase - the cell is not dividing - the cell replicates its DNA - consists of three phases, G1, S, and G2,

replication of DNA occurs in the S phase Mitotic phase - consists of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis) to form two identical cells

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Prophase - the chromatin fibers change into chromosomes

Metaphase - microtubules align the centromeres of the chromatid pairs at the metaphase plate

Anaphase - the chromatid pairs split at the centromere and move to opposite poles of the cell; the chromatids are now called chromosomes

Telophase - two identical nuclei are formed around the identical sets of chromosomes now in their chromatin form

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Division of a cell’s cytoplasm to form two identical cells

Usually begins in late anaphase The plasma membrane constricts at its

middle forming a cleavage furrow The cell eventually splits into two daughter

cells Interphase begins when cytokinesis is

complete

1

Pericentriolar material

Nucleolus Nuclear envelope Chromatin Plasma membrane

Cytosol

(a) INTERPHASE

Centrioles

Centrosome:

all at 700x LM

1

Late Early

Pericentriolar material

Nucleolus Nuclear envelope Chromatin Plasma membrane

Cytosol

Chromosome (two chromatids

joined at centromere

(a) INTERPHASE

(b) PROPHASE

Centrioles

Centrosome:

Fragments of nuclear envelope

Mitotic spindle (microtubules)

Kinetochore

2

all at 700x LM

Centromere

1

Pericentriolar material

Nucleolus Nuclear envelope Chromatin Plasma membrane

Cytosol

Metaphase plate

(a) INTERPHASE

Centrioles

Centrosome:

(c) METAPHASE

2

3

Late Early (b) PROPHASE

Fragments of nuclear envelope

Mitotic spindle (microtubules)

Kinetochore

all at 700x LM

Chromosome (two chromatids

joined at centromere

Centromere

1

Early Late

(d) ANAPHASE

Pericentriolar material

Nucleolus Nuclear envelope Chromatin Plasma membrane

Cytosol

Chromosome

(a) INTERPHASE

Centrioles

Centrosome:

(c) METAPHASE

2

3

4

Cleavage furrow

Late Early (b) PROPHASE

Fragments of nuclear envelope

Mitotic spindle (microtubules)

Kinetochore

Metaphase plate

all at 700x LM

Chromosome (two chromatids

joined at centromere

Centromere

1

Early Late

(d) ANAPHASE

Pericentriolar material

Nucleolus Nuclear envelope Chromatin Plasma membrane

Cytosol

(a) INTERPHASE

Centrioles

Centrosome:

Cleavage furrow

(e) TELOPHASE

(c) METAPHASE

2

3

4

5

Cleavage furrow

Late Early (b) PROPHASE

Fragments of nuclear envelope

Mitotic spindle (microtubules)

Kinetochore

Metaphase plate

Chromosome

all at 700x LM

Chromosome (two chromatids

joined at centromere

Centromere

1

Early Late

(d) ANAPHASE

Pericentriolar material

Nucleolus Nuclear envelope Chromatin Plasma membrane

Cytosol

(a) INTERPHASE

Centrioles

Centrosome:

(f) IDENTICAL CELLS IN INTERPHASE

Cleavage furrow

(e) TELOPHASE

(c) METAPHASE

Cleavage furrow

2

3

4

5

6

Late Early (b) PROPHASE

Fragments of nuclear envelope

Mitotic spindle (microtubules)

Kinetochore

Metaphase plate

Chromosome

all at 700x LM

Centromere

Chromosome (two chromatids

joined at centromere

Mitosis

Mitosis

During sexual reproduction each new organism is the result of the union of two gametes (fertilization), one from each parent

Meiosis - reproductive cell division that occurs in the gonads (ovaries and testes) that produces gametes with half the number of chromosomes

Haploid cells - gametes contain a single set of 23 chromosomes

Fertilization restores the diploid number of chromosomes (46)

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Meiosis occurs in two successive stages: meiosis I and meiosis II

Each of these two stages has 4 phases: prophase, metaphase, anaphase, and telophase

Summary - Meiosis I begins with a diploid cell and ends with two cells having the haploid number of chromosomes; in Meiosis II, each of the two haploid cells divides, the net result is four haploid gametes that are genetically different from the original diploid starting cell

Meiosis

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The average adult has nearly 100 trillion cells

There are about 200 different types of cells

Cells come in a variety of shapes and sizes

Cellular diversity permits organization of cells into more complex tissues and organs