Download Intro to Biology * Lecture 40

Bell Work
• What does each of the following cell parts do?
• When compared to a factory, what would be
there job?
• Nucleus
• Cell Membrane
• Cell Wall
• Cytoplasm (cytosol)
Intro to Biology – Lecture 40
Inside the Nucleus
Inside the Nucleus
The Nucleolus
• A non-membrane bound structure and is the
center of the cell composed of proteins and
nucleic acids.
The Nucleolus
• Its function is to transcribe ribosomal RNA
(rRNA) and assemble it within the cell.
• It takes up to about 25% of the nuclear
volume.
Nucleoplasm
• Found inside of the nucleus
• No big organelles
• Holds the chromatin and nucleolus
During Cell Division
• When the nuclear membrane disappears, so
does the nucleoplasm.
• When the cell nucleus has reformed, the
nucleoplasm fills the space again.
Chromosomes
• Carry all of the information used to help a cell
grow, thrive, and reproduce.
• Made of DNA
• Segments of DNA in specific patterns are
called genes.
• In a factory, chromosomes would be the
“record books”.
Chromatin
• The uncoiled form of chromosomes
• Just before reproduction, chromatin
condenses to form chromosomes.
Number of Chromosomes
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Humans have 46 chromosomes (23 pairs).
Peas only have 12. A dog has 78.
There is a crayfish with 200 chromosomes.
The number of chromosomes is NOT related
to the intelligence or complexity of the
creature.
What do Chromosomes do?
• Chromosomes work with nucleic acids in the
cell to build proteins and help in cell division.
• mRNA in the nucleus with the DNA
• tRNA is found outside of the nucleus in the
cytosol
Diploid Cells
• Cells with two complete sets of chromosomes
Haploids
• Cells with only one set of chromosomes
• Found in cells involved in sexual reproduction
• Created in meiosis
Centrioles
• Help with cell division (both mitosis and
meiosis)
• Cannot be seen when the cell is not dividing
• Made of microtubules
Centriole Structure
• a small set of microtubules arranged in a
specific way
• Found in pairs and move towards opposite
ends of the nucleus when it is time for cell
division
• During division, threads (called the mitotic
spindle) are attached to the centrioles
Microtubules
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Thick Protein Tubes
Strong spirals of thousands of subunits
Subunits are made of the protein tubulin
They are like the secretaries of the factory.
They have many small jobs dealing in the
nucleus (command center).
One of their Jobs – Cell Division
• They connect to chromosomes, help them
with their first split, and then move to each
new daughter cell.
• Once the cell has finished dividing, the
microtubules are put to work in other places.
Between Cell Divisions
• Cannot see centrioles
• Instead You will see a condensed and darker
area called the centrosome.
Centrioles Job During Cell Division
• Interphase - the cell is at rest until the the
centrioles duplicate.
• Prophase - centrioles move to opposite ends
of the nucleus and a mitotic spindle of threads
begins to appear.
• Metaphase - Threads connect to the
chromosomes.
• Anaphase - Chromosomes are split and pulled
towards each centriole.
• Telophase - Chromosomes begin to unravel
and new nuclear envelopes begin to appear.
• The centrioles have done their job.