Chromosome structure v2

Chromosome structure

1. Chromosome
Structure

2. Bacterial Chromosome Structure
•Prokaryotic cells (bacteria) contain their
chromosome as circular DNA.
•Usually the entire genome is a single circle, but
often there are extra circles called plasmids.
•The DNA is packaged by DNA-binding
proteins.

3. The bacterial DNA is packaged in loops back and forth.
The bundled DNA is called the nucleoid.
It concentrates the DNA in part of the cell, but it is not separated by a nuclear
membrane (as in eukaryotes.)
The DNA does form loops back and forth to a protein core, attached to the
cell wall.

4. In eukaryotic cells, DNA is bundled
into structures called
chromosomes.

5. •The DNA molecule is
threaded so fine that
it is only possible to
see it under powerful
electron microscopes.
•http://www.cytochemistry.net/Cell-
biology/nucleus2.htm

6. But, during cell division:
•
www.answers.com/topic/mitosis

7. What is a chromosome?
•Most of what researchers know about chromosomes was
learned by observing chromosomes during cell division.
•In the nucleus of each dividing cell, the DNA molecule is
packaged into thread-like structures called
chromosomes.
•Chromosomes are not visible in the cell’s nucleus—not
even under a microscope—when the cell is not dividing.
–Cell Nuclei
•However, the DNA that makes up chromosomes
becomes more tightly packed during cell division and is
then visible under a microscope.

8. How is DNA packed into
chromosomes?
•Each chromosome is made up of DNA
tightly coiled many times around proteins
called histones that support its structure.
http://www.cytochemistry.net/Cell-biology/nucleus2.htm
http://biology.kenyon.edu/courses/biol114/Chap01/
chrom_struct.html

9. DNA
Nucleosomes
solenoid (nucleoprotein fibers)
Extended chromosome fibers
Condensed chromosome scaffold
Chromosome

10. •Each chromosome has a
constriction point called
the centromere, which
divides the chromosome
into two sections, or
“arms.”
•The short arm of the
chromosome is labeled
the “p arm.” The long arm
of the chromosome is
labeled the “q arm.”
•The location of the
centromere on each
chromosome gives the
chromosome its
characteristic shape, and
can be used to help
describe the location of
specific genes.
http://ghr.nlm.nih.gov/handbook/
illustrations/chromosomestructure

11. http://www.biologycorner.com/bio1/celldivision-chromosomes.html
chromosome animation