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CMMB 403 Study Guide - Comprehensive Final Exam Guide - Messenger Rna, Embryo, Protein


Department
Cellular, Molecular and Microbial Biology
Course Code
CMMB 403
Professor
John Cobb
Study Guide
Final

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CMMB 403

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Introductory Lecture
- We are still in the early stages of learning how the genome encodes the instructions to make
an animal accordingly to the cytoplasm
- Model organisms are the basic molecular and biochemical tools of development which hold
likeness in all animals, with variations that generate different outcomes
- Example: C. elegans, mouse, zebrafish
- Video
- Cleavage is when a cell divides a lot
- In the first 4 - 5 weeks of pregnancy, the embryo begins to develop its organs
- It takes approximately 5 days to form a blastocyst
- Outer cells form to become the placenta and the inner cells form to become the organism
- The inner cells form a disc, which is when pregnancy is initiated
- This disc changes the geographical locations of cells in the outer layer
- Disc forms the actual embryo, which is formed at 15 days of development
- Disc develops a hollow tube, which goes on to become the spinal cord, and in its initial
stages, creates two openings, which become the mouth and anus of the organism
- Gastrulation is when cells start to move
- The disc helps form the 3 germ layers: endoderm, mesoderm, and ectoderm
HOW IS THE GENOME TRANSLATED INTO FUNCTION OR PHENOTYPE?
- The genome contains nearly 25,000 protein-coding genes which get transcribed into many
RNAs, which are further translated into proteins which can have multiple variations
- These variations in protein order is what gives different creatures their individual
characteristics
- If transcription and translation are completed correctly and in a controlled manner, with proper
protein modifications in time and space, an animal forms from a single cell
HOW DOES THE GENOME DIRECT PROPER DEVELOPMENT?
- By removing the function of a gene (ie. inactivating the gene) and seeing the effects on the
model organism, scientists can determine the role and contribution of the gene in
development and the resulting phenotype
- Example: Holt-Oram syndrome
- Forelimb and heart defects
- People with this syndrome often are found to be missing their radius bone in their limbs,
and also have digit defects. As for the heart, they can have holes in different chambers of
their heart
- Found to be the result of a mutation of one copy of a gene called TBX5
- This gene, TBX5 codes for a transcription factor
- Haploinsufficiency is when one functional copy of a gene is not enough to provide enough
protein for normal function
- Essentially, haploinsufficiency is when only 1/2 genes coding for a phenotype are active
and thus there is not enough proteins being made to display the phenotype properly
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- Example: People with Holt-Oram syndrome have 1 gene, out of 2 that are there, not being
expressed, therefore leading to those individuals having that syndrome
THE IMPORTANCE OF LOCATION
- First clue to function: where a given gene is expressed during development
- Technique: Whole-mount In Situ Hybridization (WISH) on right is a method used to
determine where in an embryo a certain gene is transcribed
- Procedure:
- Step 1: Add a labeled probe1 to
fixed embryos
- The probe hybridizes to
complementary mRNA
- Step 2: Detect probe with antibody
- Step 3: Antibody has enzyme
attached which turns substrate
purple, revealing where the gene is expressed
- Image on right: dark purple
spots show where the gene
is being expressed, and
thus, what body part that
gene will affect if mutated
or found to be
haploinsufficient
- Tbx5 is only expressed in
the forelimbs and is
detected by WISH in the
heart and forelimbs in
mouse embryo, this explains why there are only defects in the forelimbs, not hindlimbs
- A mouse model: Tbx5 knocked out in limbs
- Found an absence of forelimb skeletal elements in newborn Tbx5 mutant pups
1 probe is a piece of RNA and degoxigenin
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