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

• 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

• 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.