1. CELLS: THE LIVING UNITS
CHAPTER # 3(d)
CELLS: THE LIVING UNITS

2. Defines changes from formation of the cell until it reproduces
Cell Cycle
Defines changes from formation of the cell until it reproduces
Includes:
Interphase
Cell division (mitotic phase)

3. Period from cell formation to cell division
Interphase
Period from cell formation to cell division
Nuclear material called chromatin
Four subphases:
G1 (gap 1)—vigorous growth and metabolism
G0—gap phase in cells that permanently cease dividing
S (synthetic)—DNA replication
G2 (gap 2)—preparation for division

4. S Growth and DNA synthesis
G1 checkpoint
(restriction point) S
Growth and DNA
synthesis G2
Growth and final
preparations for
division G1
Growth M
G2 checkpoint
Figure 3.31

5. Centrosomes (each has 2 centrioles) Interphase Plasma membrane
Nucleolus
Chromatin
Nuclear
envelope
Interphase
Figure 3.33

6. DNA Replication
DNA helices begin unwinding from the nucleosomes
Helicase untwists the double helix and exposes complementary chains
The Y-shaped site of replication is the replication fork
Each nucleotide strand serves as a template for building a new complementary strand

7. DNA polymerase only works in one direction
DNA Replication
DNA polymerase only works in one direction
Continuous leading strand is synthesized
Discontinuous lagging strand is synthesized in segments
DNA ligase splices together short segments of discontinuous strand

8. DNA Replication
End result: two DNA molecules formed from the original
This process is called semiconservative replication

9. template for synthesis of new strand Free nucleotides DNA polymerase
Old strand acts as a
template for synthesis
of new strand
Free nucleotides
DNA polymerase
Chromosome
Leading strand
Two new strands (leading and lagging)
synthesized in opposite directions
Lagging
strand
Old DNA
Helicase unwinds
the double helix and
exposes the bases
Replication
fork
Adenine
Thymine
Cytosine
DNA polymerase
Old (template) strand
Guanine
Figure 3.32

10. DNA Replication
PLAY
Animation: DNA Replication

11. Mitotic (M) phase of the cell cycle
Cell Division
Mitotic (M) phase of the cell cycle
Essential for body growth and tissue repair
Does not occur in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle

12. Includes two distinct events:
Cell Division
Includes two distinct events:
Mitosis—four stages of nuclear division:
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis—division of cytoplasm by cleavage furrow

13. S Growth and DNA synthesis
G1 checkpoint
(restriction point) S
Growth and DNA
synthesis G2
Growth and final
preparations for
division G1
Growth M
G2 checkpoint
Figure 3.31

14. Cell Division
PLAY
Animation: Mitosis

15. Prophase
Chromosomes become visible, each with two chromatids joined at a centromere
Centrosomes separate and migrate toward opposite poles
Mitotic spindles and asters form

16. Prophase
Nuclear envelope fragments
Kinetochore microtubules attach to kinetochore of centromeres and draw them toward the equator of the cell
Polar microtubules assist in forcing the poles apart

17. Early mitotic Early Prophase spindle Aster Chromosome Centromere
consisting of two
sister chromatids
Centromere
Early Prophase
Figure 3.33

18. Polar microtubule Spindle pole Late Prophase Fragments of nuclear
envelope
Kinetochore
Kinetochore
microtubule
Late Prophase
Figure 3.33

19. Metaphase
Centromeres of chromosomes are aligned at the equator
This plane midway between the poles is called the metaphase plate

20. Metaphase
Spindle
Metaphase
plate
Metaphase
Figure 3.33

21. Anaphase
Shortest phase
Centromeres of chromosomes split simultaneously—each chromatid now becomes a chromosome
Chromosomes (V shaped) are pulled toward poles by motor proteins of kinetochores
Polar microtubules continue forcing the poles apart

22. Anaphase
Daughter
chromosomes
Anaphase
Figure 3.33

23. Telophase
Begins when chromosome movement stops
The two sets of chromosomes uncoil to form chromatin
New nuclear membrane forms around each chromatin mass
Nucleoli reappear
Spindle disappears

24. Cytokinesis
Begins during late anaphase
Ring of actin microfilaments contracts to form a cleavage furrow
Two daughter cells are pinched apart, each containing a nucleus identical to the original

25. Telophase and Cytokinesis
Nuclear
envelope
forming
Nucleolus
forming
Contractile
ring at
cleavage
furrow
Telophase and Cytokinesis
Telophase
Figure 3.33

26. Control of Cell Division
“Go” signals:
Critical volume of cell when area of membrane is inadequate for exchange
Chemicals (e.g., growth factors, hormones, cyclins, and cyclin-dependent kinases (Cdks))

27. Control of Cell Division
“Stop” signals:
Contact inhibition
Growth-inhibiting factors produced by repressor genes

28. DNA is the master blueprint for protein synthesis
Gene: Segment of DNA with blueprint for one polypeptide
Triplets of nucleotide bases form genetic library
Each triplet specifies coding for an amino acid
PLAY
Animation: DNA and RNA

29. Nuclear envelope DNA Transcription RNA Processing Pre-mRNA mRNA
pores
Ribosome
Translation
Polypeptide
Figure 3.34

30. Roles of the Three Main Types of RNA
Messenger RNA (mRNA)
Carries instructions for building a polypeptide, from gene in DNA to ribosomes in cytoplasm

31. Roles of the Three Main Types of RNA
Ribosomal RNA (rRNA)
A structural component of ribosomes that, along with tRNA, helps translate message from mRNA

32. Roles of the Three Main Types of RNA
Transfer RNAs (tRNAs)
Bind to amino acids and pair with bases of codons of mRNA at ribosome to begin process of protein synthesis