Cells work together to carry out complex functions

5.5 Multicellular Life

Multicellular organisms depend on interactions among different cell types.

• Tissues - groups of cells that perform a similar function.• Organs - groups of tissues that perform a specific or similar

function.• Organ systems - groups of organs that carry out similar

functions.• Cells Tissues Organs Organ Systems

CELL TISSUE ORGAN

5.5 Multicellular Life

Specialized cells perform specific functions.• Cells develop into their mature forms through the process of

Differentiation.• Cells differ because different combinations of genes are

expressed.• A cell’s location in an embryo helps determine how it will

differentiate.

Outer: skin cells Middle: bone cells Inner: intestines

5.5 Multicellular Life

Stem cells• have the ability to

– divide and renew themselves and remain undifferentiated

OR– develop into a variety of specialized cell types

5.5 Multicellular Life

• 3 types of stem cells

1. Totipotent - grow into any other cell type including another stem cell

2. Pluripotent - grow into any cell type but a totipotent cell

3. Multipotent - grow into cells of a closely related cell family

5.5 Multicellular Life

First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules.

• Stem cells come from adults and embryos.

– Adult stem cells can be hard to isolate and grow.– Adult stem cells may prevent transplant rejection.– Embryonic stem cells raises ethical issues

5.5 Multicellular Life

• The use of stem cells offers many potential benefits.

– used to treat leukemia and lymphoma.– may cure disease or replace damaged organs.– may revolutionize the drug development process.

5.5 Multicellular Life

Chromosome – rod-shaped structures made of

DNA & protein • Histones – (protein) help maintain the shape of the chromosome

and aid in the tight packing of DNA

DNA doublehelix

DNA andhistones

Chromatin SupercoiledDNA

5.2 Mitosis and Cytokinesis

• One half of a duplicated chromosome is a chromatid.

• Sister chromatids are held together at the centromere.

• Telomere – (4) the tips of the chromatids• keep the chromosome from

unwinding

5.2 Mitosis and Cytokinesis

Anatomy of a Chromosome

XTelomere

Telomere

Centromere

Chromatid Chromatid

Telomere

Telomere

Chromosome

5.2 Mitosis and Cytokinesis

Sex chromosomes – determine the sex of an organism

• X and Y • Carry genes for other characteristics• 2 sex chromosomes• Normal Females XX• Normal males XY

Autosomes – all of the other chromosomes• 44 autosomes• Two sets of each • Receive one copy of an autosome from each parent

6.1 Chromosomes and Meiosis

• Homologous - pairs of autosomes– One from each parent – have the same size and shape

and carry genes for the same traits

• Karyotype – photomicrograph of chromosomes in a dividing cell• Determine sex of individual• Determine any chromosomal

abnormalities

6.1 Chromosomes and Meiosis

QTL – Quantitative Trait Locus: address of a geneEx: 6p24.q2

P-short arm

Q-long arm

5.2 Mitosis and Cytokinesis

• Chromosomes contain many genes.– Genes located close together on a chromosome

tend to be inherited together - genetic linkage.• allows the distance between two genes to be

calculated.

6.6 Meiosis and Genetic Variation

• Body cells = somatic cells.• Sex cells = Germ cells = gametes.

– egg and sperm– located in the ovaries and testes

body cells sex cells (sperm) sex cells (egg)

6.1 Chromosomes and Meiosis

Somatic cells are diploid• Diploid (2n) - cells have two copies of every

chromosome.• Human 2n = 46• Fertilization between egg and sperm occurs in

sexual reproduction.

6.1 Chromosomes and Meiosis

• Haploid (n) cells have one copy of every chromosome.

Human n = 23

6.1 Chromosomes and MeiosisGametes are haploid.

Sperm cell + Egg cell = Fertilized Egg

n + n = 2n

Haploid + Haploid = Diploid

Gamete + Gamete = Zygote

6.1 Chromosomes and Meiosis