W2L1

Question 1

Similarities of Cells

Answer 1

Contain nuclei (DNA)

Cytoplasm
- biochemical factories
- require energy

Enclosed in a plasma membrane

Question 2

Cells contain DNA

Answer 2

Requires lots of packaging

“contained” in a highly ordered fashion, easy access to specific portions of DNA for cellular use

> 6 000 000 000 bp in average human cell

Cells without DNA are some RBC (depends on stage, like mature blood cells do not have DNA but immature blood cells have DNA) and dead cells on top layer of skin.

Question 3

Cells Require Energy

Answer 3

Separation of DNA for replication

Replication of DNA (high-fidelity)

Production of RNA and proteins

Signal propagation via phosphorylation

ATP needs to be incorporated into DNA; the energy is maintained in the last phosphate of ATP

Question 4

Cells Function as Biochemical Factories

Answer 4

All cells will utilize the same subset of molecules to derive all their needs and carry out specific programmed functions

All cells require ATP

Question 5

Cells are Enclosed in Plasma Membranes

Answer 5

Lipids create hydrophobic barrier

Selective movement
- molecules needed to enter/ exit the cell

Dynamic structure that is physiologically active
- recognition and communication with other cells

Structure
- Cytoskeleton attaches to membrane proteins; junctions with other cells or extracellular matrix

Question 6

Cell Differences

Answer 6

Variability of Cell Shape

Organelle Number

Membrane Protein Composition

Genome expression
- different tissues

Question 7

Stages of Development

Answer 7

Zona pellucida remains around zygote as it becomes morula. Then after morula, there is cavitation and no more zona pellucida, resulting in blastocyst. The blastocyst implants into uterine wall. Then there is gastrulation.

1. Zygote
   - After 24-30 hours, it will divide into 2 cells, then 4, 8, 16…
2. Morula (32-64 cell stage, or 32 cells)
   - it continues to divide
   - Cells at centre lack nutrition and fluid; so need to feed these cells
   - as cells keep dividing, it will end up creating a cavity
3. The cavity created is blastocyst cavity aka blastocoel cavity
   - Formed by cells at the bottom of the cavity, which allows Na+ and Cl- to go through. Via osmotic pressure, this brings water and nutrients to feed the cells within the blastocyst
4. Cells on outside differentiate to trophoblast, which forms the trophectoderm and are also called outer cell mass; it forms structures like the placenta.
   - Cells on inside differentiate to inner cell mass cells aka embryoblasts. Some will form the embryo. Some ICM remain small, some elongate.
   - The ICM that remains small is hypoblasts.
   - ICM that is elongated are epiblasts
   - All cells continue to divide
5. Blastocoel and hypoblast combined create a new cavity named primitive yolk sac.
   - Above epiblast is cavity called amnion aka amniotic cavity
   - this is to give nutrition to the centre
6. Taking a cross section across epiblasts with bird’s eye view ….
   - primitive streak is a line where cells can migrate through to make 2 more disks underneath this origin disk. Primitive streak only goes across half way
   - primitive pit at inner end of primitive streak
   - primitive node on outside of primitive pit
   - primitive pit and primitive node are regions of high signalling to tell other cells what to make/differentiate into.
   - cells on either side of primitive streak will migrate underneath the disk and continue dividing, this will create 2 more cell layers from bottom to top. Endoderm forms first, then mesoderm forms second above the endoderm. Epiblast cells on very top (original) form ectoderm.
7. Three germ layers of the embryo
   - ectoderm on top
   - mesoderm in middle
   - endoderm on bottom

Note: hypoblast cells are still below endoderm; hypoblast cells do not become part of embryo, they remain with the trophoblast to become something else (like the placenta)

Question 8

How do cells move during Gastrulation?

Answer 8

Cell division: increasing the total number of building blocks

Adhesiveness: cells adhere to one another and to extracellular material via different types of specialized attachments
- Modification of these attachments can facilitate cell movement

Migration: the movement of an individual cell over a substrate

Question 9

Ectoderm

Answer 9

Exterior of embryo

1. Epidermis
2. Neurons

Question 10

Endoderm

Answer 10

Interior of embryo, precursor to gut and its appendages

1. Alveolar Cells
2. Thyroid Cells
3. Pancreatic Cells

Question 11

Mesoderm

Answer 11

precursor to muscle and CT

1. Cardiac muscle
2. Skeletal muscle
3. Smooth muscle
4. RBC
5. Tubule cells