Today’s Date Here

Objective Here!

Brainteaser

What runs all day, but never walksOften murmurs, never talksHas a bed, but never sleepsHas a mouth, but never eats??

Let’s Review• When does DNA replicate?

• Where does DNA replicate?

• What is helicase?

• What is DNA polymerase?

• Why does DNA replicate?

• Insert Link to movie Here!!!

Chromatin, Chromosomes & Genes

DNA is a Double Helix• Nucleotides

– A, G, T, C

• Sugar and phosphate form the backbone

• Bases lie between the backbone

• Held together by H-bonds between the bases

RNA vs. DNADNA

• Double stranded• Deoxyribose sugar • Bases: C,G A,T

RNA• Single stranded• Ribose sugar• Bases: C,G,A,U

Both contain a sugar, phosphate, and base.

RNA Is Largely Single-Stranded

DNA is found in the nucleus of a cell

• When the cell is not dividing the DNA is called Chromatin

Visualizing chromatin

Electron micrographs of “chromatin” preparations

When the Cell Begins to Divide.

• The chromatin begins to coil and forms Chromosomes

Chromosomes• Chromosomes are not visible in the cell’s

nucleus—not even under a microscope—when the cell is not dividing.

• However, the chromatin that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope.

• Most of what researchers know about chromosomes was learned by observing chromosomes during cell division.

What is a Chromosome

• Chromosomes are tiny threadlike structures, which are contained in the nucleus of every human cell except mature Red Blood Cells.

• Each chromosome contains DNA tightly coiled many times around proteins called histones that support its structure.

Types of Chromosomes

• In general every human cell contains 22 pairs of  chromosomes (also called autosomes) and one pair of sex chromosomes.

• Together these 46  chromosomes contain some 50 - 100,000 genes

How big are CHROMOSOMES?

Largest human chromosome: ~3 x 108 bp

How long is it?

3 x 108 bp x 3.4 Å/bp x 1 m/1010 Å = 10 x 10-2 m = 10 cm!

A typical cell = 10 m = 10 x 10-6 m

Therefore the DNA must be compacted ~104-fold

This is like fitting an 11-mile-long string into a 6-foot box

What are CHROMOSOMES?

• There are 23 pairs of chromosomes in the nucleus of any one of your cells

• 22 pairs are called autosomes

• 1 pair is called sex chromosomes

Human Karyotype as shown by chromosome painting

• in the 1950's, scientists were for the first time able to view the human chromosome. Although they appear disorganised within the cell, scientists have been able to identify them and so have numbered them from 1-22 in order of size.

Anatomy of a Chromosome

• Telomeres protect the ends.

• Centromere is at the primary constriction. It mediates chromosome cohesion, spindle attachment and chromosome segregation.

• Chromatid – one side of the chromosome

Kinetochore mediates attachment to the spindle

• Centromere (DNA segment) is at the primary constriction.

• The kinetochore is a huge, complicated protein complex with several layers.

• The outer layer provides attachment sites for microtubules.

What is a GENE?• Each chromosome carries a

couple of thousand genes.

• The basic physical and functional units of heredity are contained here.

• It is a code made up of pairs of bases carried on the DNA molecule.

http://ghr.nlm.nih.gov/info=basics/show/gene

What is a GENE?

• Many of these are common to all human beings.

• So, 99.9% of your DNA is identical to everyone else's

What is a GENE?• The remaining 0.1% influences the

differences between us– height, hair color and susceptibility to a

particular disease

• Environmental factors, such as lifestyle (for example, smoking and nutrition) also influence the way we look and our susceptibility to disease

GENOMEGENOME

The nucleus of a human cell contains between 30 000 and

40 000 genes. This complete set of genes is called the

GENOME.

http://learn.genetics.utah.edu/content/begin/tour/

How well did you do today?

Sister chromatids are attached to each other at an area called the?

a. Centrioleb. Centromerec. Spindled. chromosome

ActivitiesKaryotyping ActivityChromosome mapping

Chromosome mapshttp://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=gnd.chapter.272&ref=sidebar