1. Lecture 17 Nucleus pp91-95

2. Nucleus
Chinese hamster ovary cells

3. Nucleus Largest organelle Usually visible with the light microscope
Spherical – elliptical shape
~ 5 um in diameter
Double membrane surrounding the chromosomes & nucleolus
Most cells only have 1 nucleus

4. Multinuclear – several nuclei (2-50)
Exceptions:
Anulclear – no nucleus
mature red blood cells
Multinuclear – several nuclei (2-50)
liver cells, skeletal muscle cells, platelet producing cells, bone- dissolving cells

5. Nucleus
Contains nuclear envelope, nucleoli, chromatin, and distinct compartments rich in specific protein sets
Gene-containing control center of the cell
Contains the genetic library with blueprints for nearly all cellular proteins
Dictates the kinds and amounts of proteins to be synthesized

6. Nucleus
Figure 3.28a

7. 4.6 The nucleus is the cell’s genetic control center
The nucleus controls the cell’s activities and is responsible for inheritance
Inside is a complex of proteins and DNA called chromatin, which makes up the cell’s chromosomes
DNA is copied within the nucleus prior to cell division
The DNA within the nucleus contains genetic information that must be faithfully replicated and partitioned between two daughter cells to maintain the species.
Student Misconceptions and Concerns
1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence.
2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking.
Teaching Tips
1. Noting the main flow of genetic information on the board as DNA → RNA → protein will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, rRNA, mRNA, ribosomes, and proteins are produced in a cell.
2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the door to the boss’s office.
3. Some of your more knowledgeable students may like to guess the exceptions to the rule of 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and adult red blood cells in mammals.
4. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary working copy of the genetic material. In some ways, this is like making a working photocopy of an important document, keeping the original copy safely stored away.
Copyright © 2009 Pearson Education, Inc.

8. 4.6 The nucleus is the cell’s genetic control center
The nuclear envelope is a double membrane with pores that allow material to flow in and out of the nucleus
It is attached to a network of cellular membranes called the endoplasmic reticulum
Each of the membranes in the nuclear envelope (membrane) is a lipid bilayer separated by a space of 20–40 nm.
Student Misconceptions and Concerns
1. Students can have trouble relating many cell organelles to their diverse functions. They may not realize that Modules 4.6–4.13 introduce the primary organelles in the order that they function in the production and release of secretory proteins. Products and information generally move from the central nucleus to the rough ER, through the more peripherally located Golgi apparatus and the secretory vesicles, and finally to the outer plasma membrane. Emphasizing the flow from center to periphery in this process will help students to remember the function of individual organelles as they recall the steps of the sequence.
2. Conceptually, some students seem to benefit from the well-developed cell-factory analogy developed in the text. The use of this analogy in lecture might help to anchor these relationships. As mentioned before, challenge students to find exceptions in the analogy, an exercise that promotes critical thinking.
Teaching Tips
1. Noting the main flow of genetic information on the board as DNA → RNA → protein will provide a useful reference for students when explaining these processes. As a review, have students note where new molecules of DNA, rRNA, mRNA, ribosomes, and proteins are produced in a cell.
2. If you wish to continue the text’s factory analogy, nuclear pores might be said to function most like the door to the boss’s office.
3. Some of your more knowledgeable students may like to guess the exceptions to the rule of 46 chromosomes per human cell. These exceptions include gametes, some of the cells that produce them, and adult red blood cells in mammals.
4. If you want to challenge your students further, ask them to consider the adaptive advantage of using mRNA to direct the production of proteins instead of using DNA directly. Some biologists suggest that DNA is better protected in the nucleus and that mRNA, exposed to more damaging cross-reactions in the cytosol, is the temporary working copy of the genetic material. In some ways, this is like making a working photocopy of an important document, keeping the original copy safely stored away.
Copyright © 2009 Pearson Education, Inc.

10. Two membranes of nuclear envelope
Nucleus
Nucleolus
Chromatin
Pore
Figure 4.6 TEM (left) and diagram (right) of the nucleus.
Endoplasmic
reticulum
Ribosomes

11. Nuclear Envelope
Selectively permeable double membrane barrier containing pores
Encloses jellylike nucleoplasm, which contains essential solutes

12. Nuclear Envelope
Outer membrane is continuous with the rough ER and is studded with ribosomes
Inner membrane is lined with the nuclear lamina, which maintains the shape of the nucleus
Pore complex regulates transport of large molecules into and out of the nucleus

13. Nucleoli Dark-staining spherical bodies within nucleus
Involved in rRNA synthesis and ribosome subunit assembly
Associated with nucleolar organizer regions
Contains DNA coding for rRNA
Usually one or two per cell
© 2013 Pearson Education, Inc.

14. Surface of nuclear envelope.
Figure 3.29b The nucleus.
Surface of nuclear envelope.
Fracture
line of outer
membrane
Nuclear
pores
Nucleus
Nuclear pore complexes. Each
pore is ringed by protein particles.
Nuclear lamina. The netlike lamina
composed of intermediate filaments
formed by lamins lines the inner surface
of the nuclear envelope.
© 2013 Pearson Education, Inc.

15. Chromatin
Threadlike strands of DNA (30%), histone proteins (60%), and RNA (10%)
Arranged in fundamental units called nucleosomes
Histones pack long DNA molecules; involved in gene regulation
Condense into barlike bodies called chromosomes when cell starts to divide
© 2013 Pearson Education, Inc.

16. Figure 3.30 Chromatin and chromosome structure.
1 DNA
double
helix (2-nm
diameter)
Histones
2 Chromatin
(“beads on a string”)
structure with
nucleosomes
Linker DNA
Nucleosome (10-nm diameter;
eight histone proteins wrapped
by two winds of the DNA double
helix)
3 Tight helical fiber
(30-nm diameter)
4 Looped domain
structure (300-nm
diameter)
5 Chromatid
(700-nm diameter)
6 Metaphase
chromosome
(at midpoint
of cell division)
consists of two
sister
chromatids
© 2013 Pearson Education, Inc.

17. Nucleic Acids
Composed of carbon, oxygen, hydrogen, nitrogen, and phosphorus
Their structural unit, the nucleotide, is composed of N-containing base, a pentose sugar, and a phosphate group

18. Nucleic Acids
Five nitrogen bases contribute to nucleotide structure – adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U)
Two major classes – DNA and RNA

19. Deoxyribonucleic Acid (DNA)
Double-stranded helical molecule found in the nucleus of the cell
Replicates itself before the cell divides, ensuring genetic continuity
Provides instructions for protein synthesis

20. Structure of DNA
Figure 2.22a

21. Structure of DNA
Figure 2.22b

22. Ribonucleic Acid (RNA)
Single-stranded molecule found in both the nucleus and the cytoplasm of a cell
Uses the nitrogenous base uracil instead of thymine
Three varieties of RNA: messenger RNA, transfer RNA, and ribosomal RNA

23. Adenosine Triphosphate (ATP)
Source of immediately usable energy for the cell
Adenine-containing RNA nucleotide with three phosphate groups

24. Adenosine Triphosphate (ATP)
Figure 2.23

26. Thank you