the molecular basis of inheritance -...

PowerPoint® Lecture Presentations for

Biology

Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 16

The Molecular Basis of

Inheritance

Concept 16.3 A chromosome consists of a DNA molecule packed together with proteins

• The bacterial chromosome is a double-

stranded, circular DNA molecule associated

with a small amount of protein

• Eukaryotic chromosomes have linear DNA

molecules associated with a large amount of

protein

• In a bacterium, the DNA is “supercoiled” and

found in a region of the cell called the nucleoid

• Chromatin is a complex of DNA and protein,

and is found in the nucleus of eukaryotic cells

• Histones are proteins that are responsible for

the first level of DNA packing in chromatin

Animation: DNA Packing

Fig. 16-21a

double helix

(2 nm in diameter)

Nucleosome

(10 nm in diameter)

Histones Histone tail

DNA, the double helix Histones Nucleosomes, or “beads on a string” (10-nm fiber)

Fig. 16-21b

30-nm fiber

Chromatid (700 nm)

Loops Scaffold

300-nm fiber

Replicated chromosome (1,400 nm)

30-nm fiber Looped domains (300-nm fiber)

Metaphase chromosome

• Chromatin is organized into fibers

• 10-nm fiber

– DNA winds around histones to form nucleosome “beads”

– Nucleosomes are strung together like beads on a string by linker DNA

• 30-nm fiber

– Interactions between nucleosomes cause the thin fiber to coil or fold into this thicker fiber

• 300-nm fiber

– The 30-nm fiber forms looped domains that

attach to proteins

• Metaphase chromosome

– The looped domains coil further

– The width of a chromatid is 700 nm

• Most chromatin is loosely packed in the nucleus during interphase and condenses prior to mitosis

• Loosely packed chromatin is called euchromatin

• During interphase a few regions of chromatin (centromeres and telomeres) are highly condensed into heterochromatin

• Dense packing of the heterochromatin makes it difficult for the cell to express genetic information coded in these regions

• Histones can undergo chemical modifications

that result in changes in chromatin organization

– For example, phosphorylation of a specific

amino acid on a histone tail affects

chromosomal behavior during meiosis

Fig. 16-22

RESULTS

Condensin and

DNA (yellow)

Outline of nucleus

Condensin (green)

DNA (red at periphery)

Normal cell nucleus Mutant cell nucleus

Fig. 16-UN2

Sugar-phosphate

backbone

Nitrogenous bases

Hydrogen bond

Fig. 16-UN3

DNA pol III synthesizes

leading strand continuously

Parental

DNA DNA pol III starts DNA

synthesis at 3 end of primer,

continues in 5 3 direction

Lagging strand synthesized

in short Okazaki fragments,

later joined by DNA ligase

Primase synthesizes

a short RNA primer

Fig. 16-UN4

Fig. 16-UN5

You should now be able to:

1. Describe the contributions of the following people: Griffith; Avery, McCary, and MacLeod; Hershey and Chase; Chargaff; Watson and Crick; Franklin; Meselson and Stahl

2. Describe the structure of DNA

3. Describe the process of DNA replication; include the following terms: antiparallel structure, DNA polymerase, leading strand, lagging strand, Okazaki fragments, DNA ligase, primer, primase, helicase, topoisomerase, single-strand binding proteins

4. Describe the function of telomeres

5. Compare a bacterial chromosome and a

eukaryotic chromosome

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