lecture 5 Flashcards
1
Q
what is cell differentiation?
A
- embryonic development of multicellular organisms, zygote gives rise to cells of many different types
- cells have different structure/functions
- difference in gene expression
- morphogenesis (development of form of organism/structure)
2
Q
what are stem cells?
A
- form types of tissue (relatively unspecialised)
- reproduce indefinitely
- differentiate into specialised cells of more than one type
- totipotent stem cells (rise of any cell in an embryo/adult)
- pluripotent stem cells (differentiate into different cell types)
- multipotent stem cells (differentiate into different cell types; more limited)
3
Q
stem cells in reference to embryos vs. adults?
A
- embryonic stem cells grow easier than adult ones (theoretically give rise to all types of cells)
- range of cell types arise in adults not fully understood yet
- generate several defined types (multipotent)
- bone marrow into bone, cartilage, fate, muscle, linings of blood vessels
4
Q
how is cloning used via stem cells?
A
- organismal cloning
- somatic cell nuclear transfer (romoval of nucleus of egg replaced by another from differentiated cell)
5
Q
what is somatic cell nuclear tranfer?
A
- transplanted nucleus from tadpole cell into unucleated egg of same species
- older the donor, lower the percentage of normal tadpoles
- when from early embryo (most developed into tadpoles)
- when from fully differentiated intestinal cells of tadpole (less than 2% developed normally)
6
Q
what is reproductive cloning?
A
- dolly the sheep
- donor nuclei
- CC the cat (calico coat similar to single female parent)
- different colour/pattern due to random x chromosome inactivation
- even identical twins are slightly different
7
Q
what are faulty gene regulations in clones?
A
- nuclear transplantation shows small percentage develop normally
- many exhibit defects
- linked to epigenetic changes (differentiated cell, small number of genes in DNA turned on/expressed; regulation of gene expression relies on epigenetic change to structure of chromatin)
8
Q
what are epigenetics?
A
- cells contain entire DNA (genome)
- different cells express different genes (then different structures/functions)
- DNA code fixed but epigenome can change
- changes to expression of gene that don’t alter DNA sequence
9
Q
what are epigenetic changes?
A
- can arise from environment (smoking/stress)
- can result in chromatin changes
- epigenetic tags cause inactive genes to be tightly wrapped (inaccessible to machinery)
- active genes relaxed, easily accessible to machinery
10
Q
how do epigentic changes contribute to chromatin changes?
A
- chromatin is elaborate complex of DNA/proteins
- structure allows DNA to be packed in nucleus (important to what genes are expressed)
- histones are major proteins (first level of DNA packing)
11
Q
what are histones?
A
- major proteins (first level of DNA packing)
- groups of 8 to form nucleosomes (DNA wound twice around protein core of eight histones)
- changes to histone change gene expression
- carry chemical tags (epigenetic tags) affect histones interaction with DNA
12
Q
what are histone modifications?
A
- modifications to chromatin structure affect gene expression
- histone methylation (addition of methyl group causes condensation, reducing transcription of genes)
- histon acetylation (addition of acetyl group; opens up chromatin structure, promoting transcription)
13
Q
what is DNA methylation?
A
- different enzymes can methylate the DNA on actual bases of DNA (cytosine)
- occurs in plants, animals, fungi
- long stretches of inactive DNA (innactive x chromosomes) more methylated than regions of actively transcribed DNA
- genes not expressed are more methylated (removal of methyl group can turn on some genes)
14
Q
what is an example of DNA methylation?
A
- agouti mice (all mammals called agouti)
- two genetically identical twin mice look different
- healthy mice agouti gene methylated, not expressed
- yellow and obese for non-methylated
- genome is identical, but different epigenome
15
Q
what is epigenetic inheritance?
A
- inheritance of traits transmitted by mechanisms not involving nucleotide sequence
- chromatin modifications passed on to future generations
- once methylated, genes usually stay methylated through cell dividision
- methylation patterns passed on to daughter cells forming specialised tissues keeping chemical record og occuring during embryonic development
- most epigentic tags removed during embryo development (some not erased)
- lifestyle affects development of children modifications to chromatin (can be reversed)
