5/29/2014
1
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
5/29/2014
2
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
5/29/2014
3
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
5/29/2014
4
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
5/29/2014
5
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
5/29/2014
6
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
5/29/2014
7
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
5/29/2014
8
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
5/29/2014
9
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
5/29/2014
10
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
5/29/2014
11
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
5/29/2014
12
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
5/29/2014
13
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
5/29/2014
14
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
5/29/2014
15
5/29/2014
16
Transcription
Translation
5/29/2014
17
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
5/29/2014
18
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
5/29/2014
19
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)
5/29/2014
20
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
5/29/2014
21
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