Lecture 26: Dev of Multicellular Organisms

Question 1

Are homologous proteins functionally interchangeable

Answer 1

• yes

Question 2

Question 3

Ectoderm is precursor of

Answer 3

nervous system and epidermis

Question 4

Endoderm is the precursor of

Answer 4

gut, lung, and liver

Question 5

Mesoderm is precursor of

Answer 5

muscles and connective tissue

Question 6

Transformation of a hollow sphere of cells into a structure with a gut called _____

Answer 6

gastrulation

Question 7

Two classes of proteins most important for development

Answer 7

• Cell adhesion and cell signaling proteins
• Gene regulatory proteins

Question 8

Instructions for producing a multicellular animal contained in the __________ associated with each gene

Answer 8

Non-coding regulatory DNA

Question 9

_____ in DNA similar in most organisms but _____make one organism different from another and provide uniqueness

Answer 9

Coding sequences, non-coding sequences

Question 10

Do cells make developmental decisions long before they show any outward signs of differentiation

Answer 10

yes

Question 11

Cells that are fated to develop into a specialized cell type despite changes in envrionment are called _____

Answer 11

Determined

Question 12

Cells that can change rapidly due to alterations in environment are called

Answer 12

completely undetermined

Question 13

Cells that have some attributes of a particular cell type but can change with environment are called ______

Answer 13

committed

Question 14

Before acquiring a particular fate, cells express genes that are markers of their location, i.e. , they are

Answer 14

regionally determined

Question 15

position specific character of cell called

Answer 15

positional value

Question 16

Do cells retain memory of positional value

Answer 16

yes

Question 17

Cells can become different due to

Answer 17

asymmetric division (e.g. development of germ cells)

Question 18

Cells born the same can become different due to

Answer 18

• changes in environment after birth (different molecules induced)
  
  • These molecules then directly or indirectly alter pattern of gen expression between the 2 cells

Question 19

Induction of a different developmental program in select cells in a homogeneous group leading to altered character

Answer 19

• inductive signaling
  
  • (note few cells closest to the source take on induced character- signal is limed in time and space)
  • Types of signals:
    
    • Short range
      
      • cell-cell contacts
    • Long range:
      
      • Substances that can diffuse through the extracellular medium

Question 20

positive feedback in cell differentation

Answer 20

• System starts off homogeneous and symmetrical
• Environment imposes a weak asymmetry
• Positive feedback amplifies effect
  
  • The cell with more of product produces more while inhibiting neighbor cell
• Broken asymmetry is ‘all or none’ phenomenon
• Irreversible- once achieved external signal becomes irrelavent
• Positive feedback provides cells with memory

Question 21

long range inductive signal that imposes a pattern on a field of cells

Answer 21

Morphogen

Question 22

Morphogens are long range inductive signals that impose a pattern on a field of cells. Exert graded effects by forming gradient of different concentrations. Gradients are formed by:

Answer 22

• localized production of an inducer that diffuses away from its source
• Localized production of an inhibitor that diffuses away from its source and block the action of a uniformly distributed inducer

Question 23

Do morphogens need an ‘on’ and ‘off’ system

Answer 23

• yes
• Antagonists or extracellular inhibitors bind to the signal or its receptor and block interaction

Question 24

Signaling pathways

Answer 24

• Handful of conserved family of proteins
• Ultimate result of inductive events is change in DNA transcription
• Some genes turned ‘on’ others turned ‘off’
• Response depends on spatial and temporal expression of different sets of genes