Cell Reproduction: Chapter 10

Where do cells come from?

From other cells

Cell Theory: Rudolf Virchow (1850s): “Every cell from a cell”

What is cell division?

The production of new cells from existing cells

Before a cell divides, what must it do?

Copy its DNA

What is a genome?

All the genetic material in the cell

What are chromosomes/chromatin?

DNA + Associated proteins

What are genes?

DNA regions that code for proteins

Describe prokaryotic DNA.

One circular chromosomes

May also have plasmids

Describe eukaryotic DNA

Multiple linear chromosomes

Compare somatic and gamete cells in terms of how many chromosomes and type of each in humans.

Is somatic cells or gamete cells 1n? How about 2n?

Gamete cells are 1n while somatic cells are 2n

Why are gametes 1n or in humans 23 chromosomes while somatic cells are 2n?

Because gametes only have one set of chromosomes and that they have to pair up with another gamete to have their 2n

What is a karyotype?

Picture of chromosomes from 1 cell; arranged in homologous pairs

Each duplicated chromosomes has what?

Two identical sister chromatids.

What is a centromere?

The location of closest attachment between chromatids

What is the difference between sister chromatids and homologous chromosomes?

What is the cell doing all the time?

The cell function

What are the phases of the cell cycle and briefly describe them?

Interphase: It is where the cell spends most of its time

Grows and develops while preparing for cell division

Mitotic phase: Mitosis and cytokinesis

When the cell divides

Describe the phases of interphase and briefly describe them.

G₁: “first gap”: Cell growth

S: “synthesis”: DNA Replication

G₂: “Second gap” Cell growth and preparation for division

Checking off if it has everything ready for division such as if the DNA is replicated correctly

What is mitosis?

“Karyokinesis” Like karyotypes

Division of the nucleus and its contents

What is cytokinesis?

Division of the cytoplasm and contents

Mitosis (with cytokinesis) produces what?

Two genetically identical daughter cells

Meiosis produces what?

4 non-identical daughter cells that have half the number of chromosomes of the parent daughter cells

What is the difference between haploid and diploid cells?

Haploid -

Gametes

1n

26 chromosomes (humans)

Diploid -

Somatic cells

2n

23 chromosomes (humans)

What are the phases of mitosis?

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

Interphase (G₂): before mitosis starts.

Cells grow, replenish energy, and synthesize macromolecules

Prophase: first phase of mitosis

Nuclear envelope begins to break down

Chromosomes condense

Spindle fibers appear

Centrosomes begin to move towards opposites poles

Mitotic spindle

Microtubules and associated proteins

Starts assembly at centrosomes (centrioles in animal cells only)

Prometaphase

Chromosomes continue to condense

Kinetochores appear at the centromere, and kinetochore microtubules attach

Kinetochore

Chromosomal structure; proteins associate with specific DNA section; attachment points for microtubules

Metaphase

Mitotic spindle is fully developed

Centrosomes are at opposite poles

Chromosomes are aligned at “equatorial plate”

Kinetochore of each sister chromatid is attached spindle fiber of the opposite pole

Anaphase

Sister chromatids are pulled apart by spindle fibers and are separated (daughter chromosomes)

What is the purpose of separase?

Telophase and cytokinesis

Chromosomes arrive at opposite poles and start to decondense.

Nuclear envelope assembles

Mitotic spindle assembly breaks down and the division of the cytoplasm begins and the cells divide

What is the difference of cytokinesis in animal cells and in plant cells?

Animal cells - cleavage furrow forms from contractile ring of actin microfilaments + myosin on the cytoplasmic side of cell

Plant cell - Vesicles containing cell wall material from Golgi move along microtubules to middle of cell, forming a cell plate

How do chromosomes move?

Microtubules pull on chromosomes from opposite directions

How are daughter chromosomes moved to opposite poles? (There are 2 models)

Pac-Man: Microtubules disassembles at the kinetochore

Poleward Flux: Microtubules disassembles at the pole

Borisy Experiment (porcine kidney cells)

Microtubules labeled with yellow dye

Laser bleaches out dye in one region (mark)

Show evidence that daughter chromosomes move to opposite poles through both the Pac-Man and the Poleward Flux as the microtubules shorten from both sides but at first it was mostly evidence for the Pac-Man model

How does the kinetochores break down the microtubules?

Are all cells in the body dividing at the same rate? Give an example.

No

Example: skin cells divide at a very fast rate while liver cells divide very slowly and rarely

Are all cells in the body mitotically active? Give an example.

No

Example: Neurons and mature muscle cells

Some cells are in G₀, What does that mean?

They are not actively preparing to divide

May be temporary, may be long term (neurons, cardiac muscle)

Still performing normal cell functions

Some types of cells divide often: other types of cell _.

Do not typically divide at all

Time spent in each case of the cell cycle can what?

Vary

What triggers and coordinates events in the cell cycle?

The cell cycle control system

It responds to external and internal events

What is an external control? Give an example.

Growth factors must be present for cells to divide

Growth factors are proteins produced by certain cells that stimulate other cells to divide

Example: PDGF (platelet-derived growth factor)

What kind of receptor is the platelet derived growth factor receptor

Receptor tyrosine kinase

What are two more examples of external control and describe them?

Density-dependent inhibition - when normal cells stop dividing once they become crowded

Anchorage dependence - Normal cells must be attached to a surface to divide

What are the 3 main cell cycle checkpoints?

G₁ checkpoint

G₂ checkpoint

M checkpoint

G₁ checkpoint

Commit to mitosis or go to G_0’

Cell size? Protein reserves? DNA undamaged?

“restriction point”

G₂ checkpoint

Cell size? Protein reserves? DNA replicated?

M (Spindle) Checkpoint

Occurs at the end of metaphase

Is each sister chromatid attached to microtubule from opposite pole?

“Spindle checkpoint

Anaphase does not start until all chromosomes are properly attached to spindle at metaphase plate

What is a type of a positive regulator molecule in the cell cycle and describe it?

Cyclins and cyclin-dependent kinases (Cdks):

Involved in go-ahead signal at G₁ and G₂ checkpoints

Cdks: Active only when attached to cyclin (a protein whose concentration rises and falls within the cell during the cell cycle)

Cyclins get degraded

What are some types of a negative regulator molecule in the cell cycle? What checkpoint do they act on?

Tumor suppressor proteins: Rb (retinoblastoma), p53, and p21

Acts primarily on G₁ checkpoint

Rb (retinoblastoma)

Monitors cell size

When active (dephosphorylated), binds to transcription factors to block transcription

p53

Activated by damaged DNA

Halts the cell cycle and recruits enzymes to repair DNA

Activates apoptosis if DNA cannot be repaired

p21

Produced when levels of p53 rise

Inhibits cell division by inhibiting Cdk/cyclin complexes

Cancer

Uncontrolled cell growth

Mutations In DNA (in regions involved with cell cycle control)

Cancer cells ignore cell cycle controls

Divide excessibely

Do not exhibit density-dependent inhibition

Do not require added growth factors in vitro

“Immortal” in vitro - (Divide forever outside the body)

Henrietta Lacks

HeLa cells: 1951

Died of cervical cancer caused by HPV

Her cells were immortal and they keep dividing even after she died

Used in many laboratories and everything

What is transformation?

The conversion of a normal cell to a cancer cell

Cancer cells

My look different from normal cells

Have disrupted metabolism

Cease to carry out normal cell function

Lose their attachment to neighboring cells

Benign tumor

Abnormal cells remain at original site

Malignant tumor

Abnormal cells invade surrounding tissue

Metastasis

Abnormal cells spread to distant locations to form new tumors

Cancer sells may secrete what?

Molecules that cause blood vessels to grow toward tumors (angiogenesis)

How do normal cells become cancer cells?

When photo-oncogenes become oncogenes

Define proto-oncogenes and oncogenes.

Proto-oncogenes - Code for proteins that stimulate cell growth and division

Can become oncogenes (before cancel gene)

Oncogenes - Cancer-causing genes (cancer gene)

How does a proton-oncogene become an oncogene?

Example: mutation that allows Cdk to be activated without binding cyclin

What is a oncogene example?

ras gene

ras gene

Encodes Ras protein, a G protein that relays signal from growth factor receptor to protein kinases inside of cell, stimulating cell cycle

ras mutations occur in about 30% of human cancers (around 90% of pancreatic cancer cancers

What can happen to tumor suppressor genes that make a normal cell become a cancer cell?

When a tumor suppressor gene becomes mutated

It would code for a negative regulator protein that prevents cell division

What is the multistep model of cancer development?

Around 6 changes in DNA must occur for cell to become fully cancerous, including:

Appearance of active oncogene

Loss of function tumor suppressor gene (p53)

Activation of telomerase

What are two types of cancer treatments?

Radiation and chemotherapy

Radiation

Damages DNA

You might say that this would be worse for the cell as they would be more mutations but it actually damages DNA so much to a point that it doesn’t work anymore

Very targeted

What are 2 types of chemotherapy that helps treat cance?

Taxol and Herceptin (trastuzumab)

Taxol

Prevents microtubule depolymerization

Herceptin (Trastuzumab)

Binds to receptor on certain cancer cells, blocking their growth system and marking them for destruction for the immune system

Do prokaryotes perform mitosis?

No there is no nucleus they only binary fision

Remember: bacteria have one circular chromosomes, no histones, no nucleosomes (but still have some proteins associated with DNA)

Describe the process of binary fission.

What is the difference in cell division between prokaryotes and animal cells?