Lecture 13: Introduction and Molecular Evolution

Approximately how many cell types do humans have?

210 cell types

Approximately how many cells are in an adult human?

100 trillion cells

What properties do cells in tissues need to have in order for the organ/tissue to function properly?

cell adhesion, extracellular matrix, cell shape, cell communication, tissue homeostasis, etc.

What is cell adhesion?

cells stick to one another and the extracellular membrane

What is the extracellular matrix and basal lamina excreted by?

the cell

True or False: Organs and tissues remain the same size throughout life (when a person reaches adulthood).

true

In order to maintain tissue shape, what needs to happen?

cells must be born at the same rate the cells are dying

What is cell replacement done through?

stem cells

What are stem cells?

undifferentiated cells that divide and their progeny give rise to all of the specialized cells in a particular tissue

What are transmit amplifying cells?

cells that haven’t undergone differentiation yet

What is important to know about terminally different cells?

cells are usually done differentiating’ the cell no longer divides

What happens to stem cells when an injury occurs?

the stem cells will differenitate at a faster rate

How do stem cells divide?

stem cells divide asymmetrically

What does stem cell division give rise to?

two different cells (self-renewal) and a transmit amplifying cell

True or False: Each tissue in a human has its own particular type of stem cells.

true

What are lineages?

different types of progenitor cells from different cell lines

Adult stem cells are said to be what?

multipotent

What does it mean to be multipotent?

cells that give rise to only a specific subset of differentiated cells

Where are stem cells located?

in the stem niche

Embryonic stem cells are said to be what?

pluripotent

What does it mean to be pluripotent?

cells that can give rise to all cell types

What are cell properties within tissues?

Adopt defined shape

Express specific set of genes (differentiation)

Carry out specialized functions (terminally differentiated cells)

Replace dead cells with new ones (tissue homeostasis)

Remain distinct from cells in neighboring tissues

Adherence to each other

Coordination of activity

Communication

What are the 4 global responses to signals?

survive, grow and divide, differentiate, and cell death

True or False: Cells have different adhesion properties and cytoskeleton arrangements, which drive cell shape.

true

In what 2 instances does apoptosis normally occur?

during normal development and in response to cellular damage/DNA damage

What is cell lineage?

the series of divisions and cellular steps that a stem cell goes through to become a terminally differentiated cell

What is metastasis?

when tumors break away from normal tissues (inappropriate adhesion) and moves to other tissues (inappropriate movement)

What are some hallmarks of cancer cells?

Inappropriate growth

Inappropriate cell cycle control

Inappropriate adhesion

Inappropriate movement

Inappropriate signal response

True or False: Cancer cells don’t grow/divide faster than other cells.

true

What is faster than the rate of normal differentiation?

the rate of embryogenesis

In the developing Xenopus laevis, there is coordinated regulation of what?

Cell division

Cell adhesion

Cell movement

Cell differentiation

What is important to know about the development of the Xenopus laevis?

1 1 large fertilized cell that undergoes rapid rounds of cell division

Fast divisions occur from external fertilization

No increase in mass

In the Xenopus blastocyst, what are the cells held together in?

in “sheets” that move together as a whole

Xenopus blastocyst sheets are how thick?

two cells thick

How do the cell sheets move in the Xenopus blastocyst?

the cells move from the Dorsal lip (the lip of the blastopore) to the inside of the organism

What is the signaling center for differentiation in the Xenopus blastocyst?

the dorsal lip

What holds cells together to form sheets?

cell adhesion

What are 3 primary tissues in the Xenopus blastocyst?

ectoderm, mesoderm, and endoderm

What is important to know about the ectoderm?

the outer layer, forms the skin and outside structures, and forms the nervous system

What is important to know about the mesoderm?

the middle layer that forms structures in the middle of the organism

What is important to know about the endoderm?

the inside layer that forms the lining of the gut

What does the neural tube become?

the spinal cord and nervous system

What is neuralation?

the formation of the neural tube

What is occurring as the neural tube forms?

the sheets of cells invaginates (moves) and the sheets of cells change their adhesion properties

True or False: Many aspects of development and tissue formation can be viewed as converting sheets of cells to tubes, balls, and/or tubular solid structures.

true

What is a micelle?

a single layer of lipids

What are liposomes?

spherical lipid bilayers

Do lipid membranes determine cell shape?

no, they do not

What is important to know about membrane fluidity?

biological membranes are easily deformed, tough to break, and are partially “self-healing”

What 3 polymers make up the cytoskeleton?

actin, intermediate filaments, and microtubules

What is the role of the cytoskeleton?

provide a rigid framework to maintain the shapes of cells

What is cell motility depend on?

changing shape

What do focal adhesions do?

nail down the cell

What is the leading edge in a moving cell?

the lamellipodium

What are some examples of cell motility?

sperm, pollen, cytokinesis, locomotion, phagocytosis, axonal transport, plant cytoplasmic streaming, embryonic shape, muscle contract, tumor metastasis, etc.

How do tumors travel?

through blood vessels, the lymphatic system, and tissue invasion

What are some examples of cellular movement?

free swimming, crawling, moving sheets of cells, and neurons

What is some movement within cells?

Moving components such as organelles and mRNAs

Moving/building cytoskeleton (cell shape and crawling)

Moving the cytoskeleton for swimming and cytoplasmic streaming

What are the 2 types of cytoskeleton filaments?

microtubules and actin filaments

What is hemoglobin composed of?

2 alpha subunits and 2 beta subunits

True or False: The alpha and beta subunits of hemoglobin are related. They have similar shapes/structures but have slightly different amino acid sequences.

true

How did the alpha and Beta subunits of hemoglobin occur?

due to mutation and gene divergence

What forms gene families?

duplication and divergence of

True or False: Almost every protein is a member of a gene family.

true

What are some examples of steroid hormones?

cortisol, estradiol, testosterone, vitamin D3, etc.

What are some characteristics of the steroid hormone receptor family?

Hormone receptors float around in the cytoplasm

Steroid hormones are hydrophobic and can cross the cell membrane

Steroid hormones have a DNA, ligand, and transcription binding domain

What does TFIIA bind to?

DNA

What does TFIIA contain?

9 zinc finger domains

What does each zinc finger recognize?

3 base pairs

What are antibodies made up of?

several Ig domains and different repeats

True or False: Some proteins are made by combining different types of domains.

trues

What are some examples of domains?

chymotrypsin, urokinase, factor IX (blood clotting), and plasminogen

True or False: As organisms become more complex so do their domains.

true

Eukaryotic transcription factors are said to be what?

modular

What does modular mean?

comprising different types of domains

What process facilitates the assembly of coding regions containing domains?

exon shuffling

What is exon shuffling?

the chromosome is broken and a new gene is inserted into the chromosome; a new coding region is added to a particular gene

After exon shuffling, what happens?

the gene is transcribed, spliced, and the gene will include the domain of the inserted gene

Exon shuffling is considered what?

“a chromosomal accident”

Does exon shuffling occur in eukaryotes and prokaryotes?

no, exon shuffling only occurs in eukaryotes

Why does exon shuffling only occur in eurkaryotes?

splicing occurs primarily in eukaryotes—making the process much more efficient

Why does splicing make exon shuffling more efficient?

in prokaryotes, the new domain would have to insert in-frame and in the target gene without disrupting a particular gene (which is an unlikely event)

What does splicing allow?

allows a domain to be inserted anywhere in an intron

What are protein domains coded by?

an exon that doesn’t typically code for anything else

In protein domains, which direction do the N and C terminals face?

in different directions—allowing the linkage of many protein domains

True or False: Protein domains fold up independently of each other.

true

What are two readers of the histone code?

chromodomains and bromodomains

What do chromodomains bind to?

methylated lysines

What do bromodomains bind to?

acetylated lysines

What are some writers of the histone code?

SET and RING domains

What is a SET domain?

a lysine methylase

What is a RING domain?

a monoubiquitinlyation

What 2 domains are important for the Ras pathway?

SH2 and SH3 domains

What process facilitates the modular construction of an open reading frame, and for what purpose?

splicing and alternative splicing because splicing acts over long distances

True or False: Genes can have many enhancers; each enhancer can turn the gene on in response to a different signal or condition.

true

Where is Eve transcribed in Drosophila?

in odd segments

True or False Eve transcription in different segments is activated by different enhancers.

true

Why can genes have multiple enhancers?

enhancers can be located farther away from the promoter; there is not a specific distance that an enhancer has to be from the promoter