BIO3 Midterm 1

Difference between prokaryotic and eukaryotic cell structure

Prokaryotic has:

• plasma membrane

• ribosomes

• DNA and proteins everywhere

Eukaryotic has

• plasma membrane

• ribosomes

• DNA and proteins in nucleus

• Other cell organelles

Where does replication, transcription, and translation occur in both prokaryotic and eukaryotic cells

Prokaryotic:

• Replication: on DNA

• Transcription: on DNA

• Translation: on ribosomes in cytoplasm

Eukaryotic:

• Replication: on DNA in the nucleus

• Transcription: on DNA in the nucleus

• Translation: on ribosomes in cytoplasm

What does it mean when the plasma membrane is a semi permeable lipid bilayer?

Only few types of molecules can diffuse from outside to inside of the cell, however most molecules need the help of proteins to get across

Difference between passive and active transport?

Passive: High to low concentrations (favored); down a concentration gradient

Active: low to high concentrations (unfavored); up a concentration gradient

When will a gated channel (passive transport) be open?

When there is some kind of selective stimulus, resulting in a conformational change

Removal of stimulus can cause transport to cease

What are carriers (passive diffusion)?

Transporters that are high selective and have a specific binding site for one kind of solute, causing a sequential conformational change to release the molecule on the other side

What are pumps (active transport) used for?

Pumps are a highly selective protein that moves a solute against the gradient

Causes a conformational change, but requires energy to input

What is the endomembrane system? What membranes/organelles are included?

What: a group of membranes and organelles in eukaryotic cells that modify, package, and transport lipids and proteins, playing an important role in exocytosis and endocytosis

Included: nuclear envelope, ER, Golgi, lysosomes, vesicles, and plasma membrane

NOT INCLUDED: MITOCHONDRIA, CHLOROPLASTS

What is exocytosis?

Transportation of large molecules, lipids, and proteins to the plasma membrane and extracellular space

Is a constitutive pathway (always occurs) that operates in all cells to deliver goods

What does it mean for a cell to have regulated pathways in exocytosis?

Regulated pathways deliver components specific for that type of cell at specific times

Could include:

• specific membrane proteins

• specific soluble proteins that are secreted

What is endocytosis?

Transportation of large molecules and lipids into cells needed for cell function and recycling and degrading plasma membrane proteins

Several variations, but all include:

• plasma membrane invaginates (surrounds molecucle/particle)

• pinches off; results in intracellular vesicle (membrane bound sac)

• vesicle fuses with part of endomembrane system

Nucleus

Houses and protects DNA

Nuclear envelope

Membrane enclosing nucleus allowing materials to move in and out

Chromatin

DNA + associated proteins in the nucleus

Nucleolus

Condensed region in nucleus where ribosomes are formed

Rough ER

Transports and packages proteins; associated with ribosomes; makes secratory and membrane proteins

Smooth ER

Makes lipids

Cytoskeleton

Form mitotic spindle and maintain cell shape

Centrosome

Microtubule organizing center

Lysosome

Digests food and waste materials

Golgi

Modifies proteins

Central Vacuole

In plant cells that degrade materials and stores nutrients (what lysosomes do in animal cells)

Extracellular Matrix

In animal cells that provides structural support for membrane and cells in tissues

Plays a role in cell signaling and cell migration

Unicellular

One cell does everything

Most bacteria and archaea

Colonial/Simple Multicellular

Collections of many attached cells (usually from same genotype)

Has no division of labor and only a few distinct cell types

Complex Multicellular

Collection of many attached cells

Division of labor

Distinct cell types

Can start as one cell, but develop into a more complex multicellular organism with organs, structures, etc.

What are the benefits of being multicellular?

• Predation avoidance (too large to be eaten)

• Stress resistance (provides shelter for internal cells)

What are the 4 key features in multicellularity?

• Adhesion (cells must stick together)

• Communication (must communicate with one another)

• Dependence (cannot live on its own)

• Division of labor (formation of differentiated cells with different specialized functions)

What is a differentiated cell

A cell that has specific proteins present important for the function of that distinct cell type (specialized)

If all cells have the same DNA, how do you get different cell types?

Differential gene expression

What are the different levels eukaryotic gene expression can regulated at?

• Turning genes off and on in transcription

• regulating mRNA splicing/processing

• regulation of mRNA stability and translation

• post-translational modification of the protein (affects function, location, or stability)

What things bind together in enhancers in transcription regulation? What happnes next?

Regulatory TFs and DNA sequences

These activators then interact with the general TFs and RNA polymerase II, stimulating RNA polymerase to synthesize the mRNA, creating much higher levels of mRNA

What are enhancers?

The DNA sequences (binding sits) to which the regulatory TFs bind to to enhance or repress certain genes

Can be anywhere (unlike core promoter)

What do repressors do?

Bind to specific sequences that keep genes OFF

Can compete with activators

How can activators on enhancers stimulate transcription at a distance and from upstream/downstream?

DNA can bend, allowing activators to interact with the general TFs and RNApol II

Results in much higher levels of mRNA

Different combinations of TFs in a specialized cell vs the combination of the other turns on different genes

What are housekeeping genes?

Certain genes expressed for basic functions in all cells

Have similar expressions in all cells

Why do distinct cell types turn on different genes?

Because they have different combinations of activators

What is cleavage? What does it result in?

Cell divisions that divide early in the embryo (basically mitosis)

Results in the formation of a blastula (ball of cells)

What is gastrulation?

Action of blastula cells undergoing cell movement to rearrange into three primary layers that will produce all cell types

What are the three primary layers of a gastrula?

Ectoderm (outside)

Mesoderm (middle)

Endoderm (inside)

What is the difference between somatic and germ cells?

Somatic cells—all cells except germ cells

Germ cells—will make gametes

What is cell fate potential?

The potential cell types that a cell can produce

What is totipotent?

An unspecialized cell that has the ability to become any cell type

True or False: Zygotes are totipotent

True; it can make a whole organism, having the ability to make all cell types

True or False: the neuron is totipotent

False; it is not capable of producing any other cell types. It is already differentiated

What is cell fate specification?

Cell’s fate become more distinct and restricted in potential, but are not differentiated yet

Can differentiated cells divide?

No they can’t

What does multipotent mean?

A cell’s ability to make closely related cell types

What is cell signaling?

A mechanism of cell fate specification where one or more cells send a signal, to which it is received by one or more cells resulting in a change in cell fate

What is the inheritance of molecules/segregation of cell fate molecules?

A mechanism of cell fate specification where a cell divides and one cell inherits the cell fate molecule, resulting in a new cell fate

What are stem cells? What kinds of properties do they have?

Cells that can divide many times

Can give rise to more cells likely themselves (self renewal), can also produce other cells with different fates

What are the 3 types of cell division?

1. Divides to make two stem cells (symmetric cell division)

2. Divides to make one stem cell and one cell with different fate (asymmetric)

3. Divides to make two cells with different fates, neither being a stem cell (asymmetric)

What are multipotent stem cells?

Unspecialized cells that can self renew and differentiate into a limited range of specific specialized cell types

What is pluripotent?

Cell’s capability to develop into almost any type of cell or tissue in the body

Arrange these in order of plant cell division and formation of layers: formation of inner, middle and outer layers, cleavage divisions, fertilization, further morphogenesis and organogenesis, zygote

1. Fertilization

2. zygote

3. cleavage divisions

4. formation of inner, middle, and outer layers

5. further morphogenesis and organogenesis

What does basal and apical mean in terms of a plant?

Basal: bottom of shoot/root

Apical: tip of shoot/root

If plants have rigid cell walls and cells can’t move as in animals, how can you get morphogenesis?

Plant cells grow which can result in different shapes of cells, or the orientation of cell divisions positioning daughters side by side vs top to bottom to create the shape

What do the shoot apical meristem (SAM) form?

Since it has stem cells, SAM will form leaves and shoots with all of its specialized tissues and cell types, all 3 layers.

What do the root apical meristem (RAM) form?

Since RAM has stem cells, it will form the root system with its specialized tissues and cell types, all 3 layers

Is stem cells in SAM and RAM totipotent, multipotent, or pluripotent?

Pluripotent because these meristems can produce many cell types across all 3 layers, but cannot create a whole organism

What are progenitor cells?

Created when stem cells divide asymmetrically

They are cells specified for a new fate, but can divide (proliferate), and the resulting cells get pushed away from the niche, resulting in cells completing differentiation further (proliferation zone)

What are the differences between animal and plant development?

• Plant cells can’t move

• Animals have adult stem cell niches scattered throughout the body, with usually one stem cell type present

• Plants have SAM and RAM with multiple stem cell types in one place

Why do some plants keep growing year after year, while animals stop growing as adults?

Because plants make additional root and shoot meristems with pluripotent stem cells as they grow

What is regeneration?

the replacement of new cells, tissue, or whole organs

What is cell signaling?

Cellular mechanism where cellular signals or external stimuli are recieved by cells and causes a change within the receiving (target) cell

What are the 3 steps of cell signaling?

1. Recognition—receptor binds to signal (ligand) which activates the receptor

2. Relay through a signal transduction pathway—via intracellular signaling molecules

3. Cellular Response—caused by effector protein

What is quorum sensing?

Mechanism used by bacteria to sense overall cell population density in their surroundings and act accordingly (basically ability to sense each other)

What are the complex signal transduction cascade steps? (Can occur in any order)

1. Relay signals downstream

2. Amplify signals

3. Distribute signal

4. Feedback

5. Integration-combining information from more than one signaling pathway

Is signal binding a covalent or non-covalent interaction between the signal and receptor

Non-covalent

What does phosphorylation do to proteins in cell signaling?

It can change the shape of proteins, their activity, what molecules they interact with, etc.

What 2 steps does fertilization activate in the signal transduction pathway?

Amplification and distribution

Signals within an organism can have different ranges true or false?

True, short and long

How is long range signaling reached?

Can reach target cells through bloodstream (animals) or vascular system (plants)

Can reach target cell via neuronal transmission

How is short range signaling reached?

Signal can be secreted into extracellular space and can move (very short)

Through direct contact between adjacent cells. Either

• signal and receptor interact directly

• small molecules and ions move through pores between cells

What are 3 ways a signal is terminated?

1. The level of signal/ligand may go down from not being produced or being degraded

2. Enzymes can alter intracellular signaling molecules and de-activate them

3. Negative feedback can reduce or stop the signal transduction cascade

What are the variables being controlled in homeostasis?

Setpoint (optimal condition of variable) and sensor