Unit 6: Development and Regulation of the Cell Cycle

Question 1

Define/describe

Zygote

Answer 1

Fertilized egg
Fully undifferentiated / not specialized

Question 2

What are the types of stem cells?

Answer 2

Totipotent: Able to be any cell in the organism or its supporting tissues (embryo, placenta, etc)
* Limited to the zygote and the cells that result from the first few cell divisionse=

Pluripotent: Differentiated enough that it can no longer be part of the supporting tissues
* iPS - Induced pluripotent stem cells are adult cells that have been reverted in the lab to a pluripotent cells
* ePS - Embryonic pluripotent stem cells are those that are formed after a zygote is formed and begins to become specialized

Multipotent: Able to be a few cell types, but fairy differentiated – most common type of stem cell found in adults

Adult: Fully differentiated (and not stem cells, so don’t ask me why it’s on this flashcard)

Question 3

What three processes need to happen during an organism’s development?

Answer 3

Cell division: Production of more cells via mitosis
Cell differentiation: Sequential specialization of newly-divided cells, which alters the gene expression and the set of genes that are silenced
Morphogenesis: Patterning of the differentiated cells into the appropriate areas of the body

Question 4

Describe

Cytoplasmic determinants

Answer 4

Proteins, RNAs, and other molecules that are unequally distributed in an egg cell (and therefore in a zygote once the egg is fertilized)
After the zygote’s first cell division, the daughter cells receive different amounts of these cytoplasmic determinants, thus beginning the process of differentiation

Question 5

How do cells begin to become specialized in the early embryo?

Answer 5

Different amounts of cytoplasmic determinants start changing the gene expression of cells
Cell-to-cell contact (juxtacrine signaling!) then leads to signaling that causes the cell to continue differentiating

Question 6

Describe

Homeotic genes

These are also called Hox genes

Answer 6

“Master regulatory genes”
Their activation results in the production of transcription factors that then activate other tissue-specific genes

Question 7

List the

Cell Cycle Checkpoints

Answer 7

G1, G2, and M

Question 8

What happens during a “checkpoint” in the cell cycle?

Answer 8

• Progression through cell cycle is paused
• Cell signaling occurs to ensure that the cell has what it needs to progress and that the cell does not have any issues
• If good, the cell continues through the check point
• If not good, the cell may undergo repairs, stop further division (G₀), or apoptose (not technically a verb but I really don’t care)

Question 9

What is the restriction point? Why?

Answer 9

G₁
* Completion through the G1 checkpoint usually results in the cell undergoing the rest of the cell cycle
* Failure to pass G₁ results in G₀

Question 10

What is G₀?

Answer 10

A nondividing state

Most adult cells are programmed to stop dividing
* They may then continue to function for weeks (like many types of blood cells), months (like skin cells), or for the organism’s lifetime (like muscle cells and neurons)

Most remain in G₀ but some cell types can re-enter the cell cycle after receiving certain external signals

Question 11

Define / describe

Cyclins

Answer 11

Regulatory proteins that build up at specific point in the cell cycle, and are involved in allowing cells to progress through certain check points

Question 12

Define / describe

CDKs

Answer 12

Cyclin-dependent kinases
* Kinases that are inactive until certain cyclins build up and attach to them
* Upon binding/activation, these kinases then trigger further transduction cascades to allow cell cycle progression

Question 13

Growth factors

Answer 13

A type of ligand that results in the growth and development of target cells

Question 14

Density-dependent inhibition

Answer 14

A normal response of cells to stop growing and dividing when they are in direct contact with other cells
* Occurs due to cell-to-cell contact and signaling
* Many cancerous cells stop responding to these normal signals, and grow even when they are directly contacting other cells;
* * This is also how warts and other non-cancerous tumors can form

Question 15

Anchorage dependence

Answer 15

A normal response of cells to only grow when properly attached to a substrate (often the extracellular matrix)
* Occurs due to signaling that occurs from pressure on transmembrane proteins, which indicate that a cell is properly affixed to other tissues
* Many cancerous cells grow despite a lack of proper anchorage, which allows them to metastasize

Question 16

Define

Cancer

Answer 16

Condition of cells where they grow without the normal responses to cell cycle checkpoints or external signals (including anchorage dependence)

Question 17

Define

Tumor

Answer 17

A mass of cells that has grown without proper regard to density dependence
* Benign: Cells remain attached to the correct area of the body and are not stopping normal physiological function
* Malignant: Cells of a tumor break off and travel to other areas of the body and/or grow to the point of disrupting normal physiological function

Question 18

Define

Metastasis

Answer 18

The breaking off of a tumor from its origin to new locations in the body

Question 19

What environmental factors are associated with cancer?

Answer 19

• Carcinogens - chemicals that lead to cancer-causing mutations
• Radiation
• Viruses (Note: This is a growing field and it turns out a LOT of viruses are correlated to specific cancers!!!)

Question 20

What kind of genes can, if mutated, result in cancer?

Answer 20

Those for…
* Growth factors
* Cell-surface receptors
* Intracellular receptors
* Signaling pathway molecules
* Enzymes involved in DNA repair

Question 21

Define

Oncogene

Answer 21

Cancer causing genes

Question 22

Define and describe

Proto-oncogene

Answer 22

Normal genes that are important for cell growth and division but, when mutated, become oncogenes

Question 23

How can mutations result in the conversion of a proto-oncogene to an oncogene?

Answer 23

• Malfunctioning enzymes that affect chromatin structure can affect the incorrect expression of a proto-oncogene
• Genetic mutations that change the location of the proto-oncogene or a promoter in such a way that the gene becomes over-expressed
• Mutations of large segments of chromosomes that result in duplication of the proto-oncogene
• Mutation of the proto-oncogene or promoter itself, which leads to overactivity or an inability to be switched off

Question 24

What are tumor-suppressor genes

Answer 24

Genes that are normally involved in preventing damaged cells from progressing through the cell cycle
Examples of the functions of their gene products:
* DNA repair enzymes
* cell junctions, which hold cells to other cells or to the extracellular matrix
* breaking down or inactivating other molecules involved in increasing cell division

Question 25

Describe

ras

Answer 25

A proto-oncogene that produces a G-protein called ras
* Mutations in ras are found in about 1/3 of all types of human cancers, and about 20% of human cancers overall
* Associated with GPCRs
* Should only be turned on when a ligand binds to a GPCR, and should quickly break GTP into GDP / become deactivated
* When overactive or aberrantly active, it causes rapid division of cell

“should” refers to the normal, non-cancerous role

Question 26

Describe

p53

Answer 26

Called the “Guardian of the Genome” for its role in stopping cells with damaged DNA from dividing; one of the most important tumor suppressor genes
* Mutations in p53 are found in over half of human cancers

Produces transcription factor (p53 protein) which is involved in activating rougly 350 other genes¹, which produce molecules involved in cell signaling, including those that:
* cause the degradation of cyclins
* aid directly in DNA repair
* trigger apoptosis

¹ Fischer M. 2017. Census and evaluation of p53 target genes. Oncogene [Internet]; 36:3943-3956.