Cell Division & DNA Replication (Outline)

• Why do cells divide? • New Terms: gamete, zygote, somatic cells, germ cells, haploid, and diploid. • Types of eukaryotic cell division- Mitosis & Meiosis • Cell division of somatic cells and germ line cells. • Comparison of Mitosis & Meiosis in terms of # of cell divisions, # of daughter

cells, DNA content in comparison to mother cell, haploid/diploid state of daughter cells, genetic sameness or variability of daughter and mother cells.

• DNA replication

Sperm cell (haploid)

Nuclei containing DNA

Egg cell (haploid)

Fertilized egg with DNA from both parents

Embryo cells with copies of same inherited

DNA Offspring with traits inherited from both parents

Zygote (diploid)

Eukaryotic multi-cellular organisms • From gametes -sperm or egg (haploid) • Fertilization of sperm and egg produces zygote

(diploid) • Somatic cells- Body cells of multi-cellular

organism (diploid)

http://stevemorse.org/genetealogy/beyond.htm

Cell Division & Its Regulation

Key Roles of Cell Division • . • . Purpose: distribution of genetic material to

daughter cells

Types of cell division

Two types in eukaryotic cells: Mitosis produces genetic sameness (asexual reproduction) Meiosis produces genetic variability

(sexual reproduction)

Eukaryotic Cell division 1. Asexual reproduction (Identical cells) - Unicellular/ Amoeba - Some multi-cellular

eukaryotes plants and some animals like hydra, by budding cells

Eukaryotic Cell division ( cont’d) 2. Sexual reproduction (gametes, non-identical

cells- for genetic variety of offspring)

Most multi-cellular organisms have both asexual and sexual reproduction

Cell Reproduction in Humans Somatic cells (sameness)

Germ line cells of the gonads (variability)

Mitosis produces 2 genetically identical cells

Meiosis produces 4 genetically non-identical cells each with ½ the number of chromosomes Mitosis and

development

Multicellular diploid adults

(2n = 46)

Diploid zygote

(2n = 46) 2n

Meiosis Fertilization

Egg cell

Sperm cell

n

Haploid gametes (n = 23)

n

Cell Division • One mother cell divides into two identical

cells following an ordered sequence of events (Cell Cycle)

• Summary of event of dividing cells • Replicate the genetic material • Manufacture additional cellular content • Divide the nucleus • Separate the cytoplasm

Overall Comparison of Mitosis and Meiosis

DNA REPLICATION DNA replication depends on specific base pairing

• Starts with the separation of DNA strands • A protein enzyme uses each strand as a template to

assemble new nucleotides into complementary strands

Figure 10.4A

A T

C G

G C

A T

T A

A T

C G

G C

A T

T A

A T

C G

G C

A T

T A

A T

C G

G C

A

T

A T

C G

A C

T

A

Parental molecule of DNA

Both parental strands serve as templates

Two identical daughter molecules of DNA

Nucleotides

“Build a DNA Molecule” http://learn.genetics.utah.edu/content/molecules/builddn

a/

Each DNA strand of the double helix is oriented in the opposite direction

P

P

P

P

P

P

P

P

HO

OH

A

C

G

T

T

C

G

A

2′ 1′ 3′ 4′

5′

1′ 5′ 4′ 3′ 2′

5′ end 3′ end

3′ end 5′ end

DNA replication is a complex process • the helical DNA molecule must untwist or unwind specific DNA

sequences, origins of replication by the protein enzyme helicase

• several proteins are involved including DNA Polymerase

Figure 10.4B

G C

A T G C

A T C G

A G A

C G

C G C G

T A G

C

T A T

A A

T T

A

C G

C G

C G

T A

G

C

T

A

T A

A T

T A

T C T

http://www.dnai.org/a/index.html

– The enzyme DNA polymerase uses a single strand and makes a new complementary strand in a 5’ to 3’ direction • one daughter strand is made as a continuous piece • the other strand is synthesized as a series of short pieces

(discontinuously) which are then connected by the enzyme DNA ligase

Figure 10.5C

3′

5′ 3′

5′ 3′

5′

5′ 3′

Daughter strand synthesized continuously

Daughter strand synthesized in pieces

Parental DNA

DNA ligase

DNA polymerase molecule

Overall direction of replication

DNA Replication Detailed

• Replication of long stretches of DNA • Begins at multiple specific sites on the double helix • Tutorial: DNA Replication

Origin of replication

Two daughter DNA molecules

Parental strand

Daughter strand

Bubble