Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
21 Cards in this Set
- Front
- Back
|
Define epigenetics
|
-study of mitotically heritable changes in gene expression
-that occur without changes in DNA sequence |
|
|
What defines a cell type?
|
The set of genes expressed by the cell
|
|
|
How does a cell 'know' which genes to express?
|
-sequence specific transcription factors activate/ repress genes
-epigenetic marks |
|
|
Outline the roles played by epigenetic marks.
|
-mark beginning and end of genes
-allow pieces of information within genes to be distinguished -gives structure to chromosome - shows beginning, centre and end of chromosome - ensures chromosomes fold up correctly -alters how we read each gene -can lead to expression/ inactivation of gene or more subtle changes |
|
|
Explain why epigenetic control is important in development.
|
- Important for cell structure and differentiation
|
|
|
How are genetically identical twins formed
|
-at 2 cell stage of embryo development, splitting occurs and two separate embyos formed from same sperm and egg
|
|
|
Why is mitotic heritability of epigenetic marks important?
|
-ensures same sets of genes expressed in daughter cells
-ensures tissue homogeneity (liver cells divide to give more liver cells) -so cell identity is maintained |
|
|
What is the replacement of epigenetic marks called?
When is this necessary? |
-epigenetic reprogramming
-when tissue heterogeneity is required -when daughter cells must carry out very different function to parent cells, e.g. formation of eggs + sperm (sperm v. different to somatic cells) and formation of zygote (egg + sperm marks must be replaced by those relevant to totipotent cells |
|
|
What is chromatin?
|
DNA wrapped around histones
|
|
|
Why must DNA be wrapped around histones
|
so that the 2m molecules can be compressed into the 10 micron nucleus
|
|
|
Contrast the functions of tightly and loosely packed chromatin
|
-tight: DNA less accessible to transcription
-loose: DNA more accessible to transcription |
|
|
Define 'nucleosome'.
|
-smallest unit of chromatin
-146 bp of DNA wrapped around a histone octamer -making 1 and 3/4 turns around the octamer |
|
|
What does the histone octamer contain?
How is it locked together |
2x H2A, H2B, H3 and H4 and one H1, locking the spool together
|
|
|
Why do histones bind to DNA?
|
-they are positively charged
-because they are lysine and arginine rich -DNA is negatively charged due to electronegative oxygen in phosphate groups |
|
|
How is the chromatin arranged and stained in euchromatin?
|
-nucleosomes far apart, 'beads on a string' with linker DNA between
-open -less darkly stained |
|
|
The most open form of heterochromatin is formed from euchromatin...
|
-using interactions between H1 proteins in euchromatin to form a solenoidal 30nm fibre
|
|
|
How can further condensation occur?
When does this happen? |
-using scaffold proteins
-in interphase |
|
|
How can further condensation occur?
When does this happen? What does the chromosome look like now? |
-addition of more scaffold proteins
-in metaphase -X-shaped |
|
|
Outline the features of facultative heterochromatin.
|
-differs by cell type/ time
-associated with gene silencing -allows expression of certain genes and not others |
|
|
Outline the features of constituative heterochromatin
|
-same in all cell types
-performs structural role -found at centromeres, telomeres and portions of sex chromosomes |
|
|
The why chromosome is characterised by large amounts of...
|
-heterochromatin, apart fromtestes genes
|
