1

Chapter 2 – What abnormality at the cellular or molecular level lies behind each of the following disorders? (a) cystic fibrosis (b) neurofibromatosis and (c) syndactyly.

2

Cellular activities and abnormalities underlie our inherited traits, quirks, and illnesses

Understanding genetic diseases can suggest ways to treat the condition

Lack of

dystrophinFigure 2.1

3

Our bodies include more than 260 cell types

Somatic (body) cells have two copies of the genome and are said to be diploid

Gametes, sperm and egg cells have one copy of the genome and are haploid

Stem cells, which are diploid, can both replicate themselves and differentiate themselves for repair and replacement of specialized cells

44

55

66

Must maintain basic functions for growth and reproduction, responding to environment, and utilizing energy.

All cells can be divided into two main types

Prokaryotic cells

- Lack a nucleus

Eukaryotic cells

- Possess a nucleus and other organelles

Figure 2.2

8

Biologists recognize three broad categories of organisms based on cellular complexity

Archaea – extreme bacteria Eubacteria – more common forms of

bacteria

Eukarya – Includes both unicellular and multicellular eukaryotes; higher cells

99

The Archaea and Eubacteria are similar in that they are single-celled organisms, but they differ in certain features of their RNA and membranes. These cells lack nuclei and other organelles and therefore are categorized as prokaryotes.

Eukaryotic cells are complex, with abundant and diverse organelles that compartmentalize biochemical reactions. Human cells are therefore eukaryotic.

Cells contain four types of macromolecules

Type Examples Functions

Carbohydrates Sugars, starches Energy, structure

Lipids Fats, oils Membranes, hormones

Proteins Myosin, collagen Enzymes, structure

Nucleic Acids DNA, RNA Genetic information

1111

Enzymes are proteins that catalyze the multitude of biochemical reactions that occur in the cell.

The study of nucleic acids is key to the field of genetics.

12Figure 2.3

An Animal Cell

Surrounded by the plasma membrane

Contains:

- Cytoplasm

- Organelles

- Divide labor by partitioning certain areas or serving specific functions

An Animal Cell

Figure 2.3

Figure 2.3

14Figure 2.3

The Nucleus

The largest structure in a cell

Surrounded by a double-layered nuclear envelope

Contains:

- Nuclear pores that allow movement of some molecules in and out

- Nucleolus, which is the site of ribosome production

- Chromosomes composed of DNA and proteins

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Figure 2.3

Figure 2.4

The Nucleus

Figure 2.4

Secretion illustrates how organelles function together to coordinate the basic functions of life

Figure 2.5

Figure 2.3

Endoplasmic Reticulum (ER)

Interconnected membranous tubules & sacs

Winds from the nuclear envelope to the plasma membrane

Rough ER contains ribosomes and is involved in protein synthesis

Smooth ER does not contain ribosomes and is important in lipid synthesis

18Figure 2.3

Golgi Apparatus

Stack of flat membrane-enclosed sacs

Processing center that adds sugars forming glycoproteins and glycolipids

Site of final protein folding

Products are released into vesicles that bud off to the plasma membrane

Figure 2.3

LysosomesMembrane-bound sacs

containing > 40 types of digestive enzymes

Degrade bacteria, cellular debris, and nutrients

Tay-Sachs is an inherited lysosomal storage disorder Figure 2.6

20Figure 2.3

Peroxisomes

Sacs with outer membranes studded with several types of enzymes that:

Detoxify compounds from free radicals

Break down lipids, rare biochemicals

Synthesize bile acids

Abundant in liver and kidney cells

Figure 2.3

MitochondriaSurrounded by two

membranes

Site of ATP (energy) production

“powerhouse of cell”

Contain their own circular DNA

Human mitochondrial DNA is inherited only from the mother

Figure 2.7

Structures and Functions of Organelles

Table 2.1

Figure 2.3

Plasma Membrane

Forms a selective barrier

A phospholipid bilayer

- Phosphate end (hydrophilic)

- Fatty acid chains (hydrophobic)

Figure 2.8

Figure 2.3

Plasma Membrane

Contains proteins, glycoproteins, and glycolipids

- Important to cell function and interactions

- May be receptors

- Form channels for ions

Figure 2.9

25Figure 2.3

Faulty Ion Channels Cause Inherited Diseases

Sodium channels

- Mutations lead to absence or extreme pain

Potassium channels

- Mutations lead to impaired heart function and deafness

Chloride channels

- Mutations lead to cystic fibrosis

Figure 2.3

Cytoskeleton

A meshwork of protein rods and tubules

Includes three major types of proteins

- Microtubules

- Microfilaments

- Intermediate filaments

Figure 2.10

27Figure 2.3

Cytoskeleton Functions

Maintain cell shape

Connect cells to each other

Transport organelles and small molecules

Provide cell motility (some cell types)

Move chromosomes in cell division

Compose cilia and flagella

2828

▪ Spherocytosis is a heredity defect in the cytoskeleton of the red blood cell. An abnormal cytoskeleton protein beneath the cell membrane and causes the red blood cells to balloon out, blocking narrow blood vessels in organs.

29Figure 2.3

Cell Division and Death

Normal growth and development require an intricate interplay between the rates of two processes

Mitosis – Cell division

- Produces two somatic cells from one

Apoptosis – Cell death

- Precise genetically-programmed sequence

Figure 2.12

Figure 2.13

Figure 2.3

The Cell CycleThe sequence of events associated with cell division

G phase: Gap for growth

S phase: DNA synthesis

M phase: Mitosis (nuclear division)

Cytokinesis: Cell division

Figure 2.14

32Figure 2.3

Stages of the Cell Cycle

Interphase- Prepares for cell division

- Replicates DNA and subcellular structures

- Composed of

G1 – proteins, lipids, & carbs are produced

S – DNA and proteins are made

G2 – more proteins produced

- Cells may exit the cell cycle at G1 or enter G0, a dormant phase

Mitosis – Division of the nucleus

Cytokinesis – Division of the cytoplasm

33Figure 2.3

Replication of Chromosomes

Chromosomes are replicated during S phase prior to mitosis

The result is two sister chromatids held together at the centromere

Figure 2.15

34Figure 2.3

MitosisUsed for growth, repair, and replacement

Consists of a single division that produces two identical daughter cells

A continuous process divided into 4 phases

- Prophase

- Metaphase

- Anaphase

- Telophase

Figure 2.15

Figure 2.16

Mitosis in a Human Cell

Figure 2.3

Prophase

Replicated chromosomes condense

Microtubules organize into a spindle

Nuclear envelope and nucleolus break down

Figure 2.16

Figure 2.3

Metaphase

Chromosomes line up on the cell’s equator or metaphase plate

Spindle microtubules are attached to centromeres of chromosomes

Figure 2.16

Figure 2.3

Anaphase

Centromeres divide

Chromatids separate and become independent chromosomes

- They move to opposite ends of the cell

Figure 2.16

Figure 2.3

Telophase

Cell pinches in middle

Chromosomes uncoil

Spindle disassembles

Nuclear envelope reforms

Figure 2.16

40Figure 2.3

Cytokinesis

Cytoplasmic division occurs after nuclear division is complete

Organelles and macromolecules are distributed between the two daughter cells

Microfilament band contracts, separating the two cells

Figure 2.3

Mitosis Animation

42Figure 2.3

Cell Cycle Control

Checkpoints ensure that mitotic events occur in the correct sequence

Internal and external factors are involved

Many types of cancer result from faulty checkpoints

Figure 2.16

Cell Cycle Control

Figure 2.17

44Figure 2.3

Telomeres

Located at the ends of the chromosomes Cellular clock limits number of divisions based

on shrinking telomeres, after about 50 divisions Crowding, hormones, & growth factors are

extracellular influences on mitosis Sperm, eggs, bone marrow, and cancer cells

produce telomerase that prevent shortening of telomeres

Why is this important?

45Figure 2.3

Apoptosis

Begins when a cell receives a “death signal”

Killer enzymes called caspases are activated

-Destroy cellular components

Phagocytes digest the remains

Programmed cell death is part of normal development

Figure 2.18

Mitosis and apotosis work together to form functional body

Cancer or other disorders can result from too much mitosis, too little apotosis

Figure 2.19

Figure 2.3

Stem Cells

A stem cell divides by mitosis

- Produces daughter cells that retain the ability to divide and some that specialize

Progenitor cells do not have the capacity of self-renewal

Figure 2.22

48Figure 2.3

Stem Cells

All cells in the human body descend from stem cells via mitosis and differentiation

Cells differentiate down cell lineages by differential gene expression

Stem cells are present throughout life and provide growth and repair

Figure 2.3

Figure 2.23

50Figure 2.3

Stem Cells

Stem cells and progenitor cells are described in terms of their developmental potential

Totipotent – Can give rise to every cell type

Pluripotent – Have fewer possible fates

Multipotent – Have only a few fates

51Figure 2.3

Stem Cells in Health Care

There are 3 general sources of human stem cells

1) Embryonic stem cells – Created in a lab dish using the inner cell mass (ICM) of an embryo

2) Induced pluripotent stem (iPS) cells – Somatic cells reprogrammed to differentiate into any of several cell types

3) Adult stem cells – Tissue-specific or somatic stem cells

Figure 2.24

Stem Cells in Health Care

Figure 2.24

53Figure 2.3

Stem Cell Applications

Stem cells are being used in four basic ways

1) Discovery and development of drugs

2) Observing the earliest sign of disease

3) Treatment of disease via implants and transplants

4) Stimulating stem cells in the body via the introduction of reprogramming proteins

54Figure 2.3

Stem Cell Applications

Figure 2.25