Cell Division & DNA Replicationfaculty.sdmiramar.edu/bhaidar/Bio 107 Documents... · • Cell...
Transcript of Cell Division & DNA Replicationfaculty.sdmiramar.edu/bhaidar/Bio 107 Documents... · • Cell...
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