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Questions and Answers
In cats, the calico coloration pattern is linked to X-linked pigment genes, while in humans, it's not. What accounts for this difference?
In cats, the calico coloration pattern is linked to X-linked pigment genes, while in humans, it's not. What accounts for this difference?
- Cats have two X chromosomes, both of which can express different pigment alleles in the same cell, whereas human females inactivate one X chromosome.
- The process of X-chromosome inactivation occurs in cats but not in humans, leading to random expression of pigment alleles.
- Humans possess modifier genes that suppress the calico phenotype, whereas cats lack these genes.
- The pigmentation genes in humans are located on autosomes, not on the X chromosome, while in cats, these genes are X-linked. (correct)
Histone modifications, such as acetylation and phosphorylation, influence DNA binding. How do these modifications affect the interaction between histones and DNA?
Histone modifications, such as acetylation and phosphorylation, influence DNA binding. How do these modifications affect the interaction between histones and DNA?
- Acetylation and phosphorylation alter the conformation of DNA, making it more accessible to histones.
- Acetylation increases the positive charge of histones, strengthening their interaction with negatively charged DNA.
- Phosphorylation decreases the negative charge of DNA, leading to weaker interactions with histones.
- Acetylation neutralizes the positive charge of histones, reducing their affinity for DNA; phosphorylation introduces negative charges, potentially repelling DNA. (correct)
Histone modifications are often found on the N-terminal tails. What is the primary function of the histone N-terminal tail?
Histone modifications are often found on the N-terminal tails. What is the primary function of the histone N-terminal tail?
- Serving as a binding site for other histone proteins within the nucleosome
- Interacting with linker DNA between nucleosomes and influencing chromatin compaction (correct)
- Initiating DNA replication by recruiting replication factors to specific sites on the DNA
- Supporting structural stability of the nucleosome core particle
If histone acetylation leads to looser DNA packaging and increased transcriptional activity, what would be the likely effect of inhibiting histone deacetylases (HDACs)?
If histone acetylation leads to looser DNA packaging and increased transcriptional activity, what would be the likely effect of inhibiting histone deacetylases (HDACs)?
How do enzymes that add or remove chemical groups to/from amino acid residues in the histone tails play a crucial role in gene expression?
How do enzymes that add or remove chemical groups to/from amino acid residues in the histone tails play a crucial role in gene expression?
Which of the following best describes the histone code?
Which of the following best describes the histone code?
How does acetylation of histone tails typically affect DNA?
How does acetylation of histone tails typically affect DNA?
What is the primary function of histone deacetylases?
What is the primary function of histone deacetylases?
Which of the following modifications is most closely associated with the formation of heterochromatin?
Which of the following modifications is most closely associated with the formation of heterochromatin?
If a mutation prevents a cell from methylating its histones, what is the most likely outcome?
If a mutation prevents a cell from methylating its histones, what is the most likely outcome?
A researcher is studying a gene that is highly expressed in one tissue type but completely silent in another. Which epigenetic mechanism is most likely responsible for this difference?
A researcher is studying a gene that is highly expressed in one tissue type but completely silent in another. Which epigenetic mechanism is most likely responsible for this difference?
Which of the following scenarios would result in the LEAST amount of transcriptional activity?
Which of the following scenarios would result in the LEAST amount of transcriptional activity?
A drug that inhibits histone deacetylases (HDACs) is introduced to cells. What is the most likely effect on gene expression?
A drug that inhibits histone deacetylases (HDACs) is introduced to cells. What is the most likely effect on gene expression?
Which histone modification generally leads to transcriptional activation by opening up the DNA structure?
Which histone modification generally leads to transcriptional activation by opening up the DNA structure?
Histone deacetylases (HDACs) are associated with which of the following processes?
Histone deacetylases (HDACs) are associated with which of the following processes?
Methylation of histone tails is typically associated with what?
Methylation of histone tails is typically associated with what?
What is the direct effect of histone acetylation on chromatin structure?
What is the direct effect of histone acetylation on chromatin structure?
During which process is phosphorylation of histones primarily observed?
During which process is phosphorylation of histones primarily observed?
What role does Histone H1 play in nucleosome compaction?
What role does Histone H1 play in nucleosome compaction?
A mutation inhibits histone acetyltransferase (HAT) activity in a cell. What is the most likely outcome?
A mutation inhibits histone acetyltransferase (HAT) activity in a cell. What is the most likely outcome?
Which of the following modifications is most likely to result in the formation of heterochromatin?
Which of the following modifications is most likely to result in the formation of heterochromatin?
How does acetylation affect the accessibility of DNA to RNA polymerases?
How does acetylation affect the accessibility of DNA to RNA polymerases?
If a drug inhibits histone phosphorylation during cell division, what is the most likely consequence?
If a drug inhibits histone phosphorylation during cell division, what is the most likely consequence?
Which of the following best describes the immediate effect of a drug that inhibits new transcription on gene expression?
Which of the following best describes the immediate effect of a drug that inhibits new transcription on gene expression?
How does phosphorylation typically regulate H1 histone function within chromatin structure?
How does phosphorylation typically regulate H1 histone function within chromatin structure?
What is the expected outcome on gene expression when a deacetylase removes acetyl groups from H4 histones?
What is the expected outcome on gene expression when a deacetylase removes acetyl groups from H4 histones?
How does the methylation of CpG islands typically affect gene expression in eukaryotes?
How does the methylation of CpG islands typically affect gene expression in eukaryotes?
What effect do you expect on gene expression if an inversion moves a gene from a euchromatic region to a heterochromatic region?
What effect do you expect on gene expression if an inversion moves a gene from a euchromatic region to a heterochromatic region?
A researcher observes that a particular gene is more actively transcribed in liver cells compared to brain cells. Which of the following chromatin states is most likely to be observed at this gene's location in liver cells, compared to brain cells?
A researcher observes that a particular gene is more actively transcribed in liver cells compared to brain cells. Which of the following chromatin states is most likely to be observed at this gene's location in liver cells, compared to brain cells?
Which of the following is a characteristic of facultative heterochromatin but NOT constitutive heterochromatin?
Which of the following is a characteristic of facultative heterochromatin but NOT constitutive heterochromatin?
What is the primary purpose of chromosome decondensation during interphase?
What is the primary purpose of chromosome decondensation during interphase?
What is the primary characteristic of constitutive heterochromatin?
What is the primary characteristic of constitutive heterochromatin?
What is the 'position effect' related to heterochromatin?
What is the 'position effect' related to heterochromatin?
What is the role of barrier sequences in the genome?
What is the role of barrier sequences in the genome?
What is a key difference between constitutive and facultative heterochromatin?
What is a key difference between constitutive and facultative heterochromatin?
What is the purpose of X chromosome inactivation in mammals?
What is the purpose of X chromosome inactivation in mammals?
What is a Barr body?
What is a Barr body?
According to the Lyon hypothesis, when does X chromosome inactivation occur?
According to the Lyon hypothesis, when does X chromosome inactivation occur?
During interphase, which characteristic distinguishes euchromatin from heterochromatin?
During interphase, which characteristic distinguishes euchromatin from heterochromatin?
Why are adult mammalian females considered genetic mosaics with respect to X-linked genes?
Why are adult mammalian females considered genetic mosaics with respect to X-linked genes?
If a gene located in a region of heterochromatin is moved to a region of euchromatin, what is a likely outcome?
If a gene located in a region of heterochromatin is moved to a region of euchromatin, what is a likely outcome?
Which of the following is a key difference between constitutive and facultative heterochromatin?
Which of the following is a key difference between constitutive and facultative heterochromatin?
What happens to the heterochromatized X chromosome in germ cells before meiosis?
What happens to the heterochromatized X chromosome in germ cells before meiosis?
What is the primary function of heterochromatin located at the telomeres of chromosomes?
What is the primary function of heterochromatin located at the telomeres of chromosomes?
In a female with three X chromosomes, how many Barr bodies would be present in her somatic cells, assuming normal X-inactivation?
In a female with three X chromosomes, how many Barr bodies would be present in her somatic cells, assuming normal X-inactivation?
DNA methylation is associated with which type of chromatin and gene expression state?
DNA methylation is associated with which type of chromatin and gene expression state?
Which of the following statements accurately describes the randomness of X-inactivation?
Which of the following statements accurately describes the randomness of X-inactivation?
How do the replication timing differ between heterochromatin and euchromatin during the cell cycle?
How do the replication timing differ between heterochromatin and euchromatin during the cell cycle?
What occurs after an X chromosome is inactivated in a cell?
What occurs after an X chromosome is inactivated in a cell?
Telomeres in many plants are composed of?
Telomeres in many plants are composed of?
Imagine a cell where a mutation prevents the formation of heterochromatin. What would be the most likely consequence?
Imagine a cell where a mutation prevents the formation of heterochromatin. What would be the most likely consequence?
A researcher is studying a gene that is expressed during embryonic development but silenced in adult cells. Which type of chromatin modification is most likely responsible for this silencing?
A researcher is studying a gene that is expressed during embryonic development but silenced in adult cells. Which type of chromatin modification is most likely responsible for this silencing?
A gene normally located in euchromatin is moved to a position near heterochromatin due to chromosomal translocation. What is the likely outcome?
A gene normally located in euchromatin is moved to a position near heterochromatin due to chromosomal translocation. What is the likely outcome?
In calico cats, the different colors are due to?
In calico cats, the different colors are due to?
What characteristic of constitutive heterochromatin makes it useful in maintaining genome stability?
What characteristic of constitutive heterochromatin makes it useful in maintaining genome stability?
If a drug prevents DNA methylation, what is the most likely effect on genes within heterochromatic regions?
If a drug prevents DNA methylation, what is the most likely effect on genes within heterochromatic regions?
Which of the following best describes the structural organization of interphase chromosomes regarding heterochromatin and euchromatin?
Which of the following best describes the structural organization of interphase chromosomes regarding heterochromatin and euchromatin?
How might changes in heterochromatin structure contribute to the aging process?
How might changes in heterochromatin structure contribute to the aging process?
A scientist discovers a mutation that disrupts the boundary between a heterochromatic region and a euchromatic region. What is the most likely consequence?
A scientist discovers a mutation that disrupts the boundary between a heterochromatic region and a euchromatic region. What is the most likely consequence?
Which of the following mechanisms is NOT directly involved in the formation or maintenance of heterochromatin?
Which of the following mechanisms is NOT directly involved in the formation or maintenance of heterochromatin?
In a study comparing the genomes of different cell types within the same organism, what would you expect to find regarding heterochromatin distribution?
In a study comparing the genomes of different cell types within the same organism, what would you expect to find regarding heterochromatin distribution?
Flashcards
Why are there no calico women?
Why are there no calico women?
X-linked pigment genes cause calico patterns in cats. Humans don't have these pigment genes on the X chromosome.
Histone Modifications
Histone Modifications
Post-translational modifications to histone tails by enzymes, involving adding or removing chemical groups.
Strong Histone Interaction
Strong Histone Interaction
If the interaction is very strong, the DNA is compacted and there is no activity.
Weak Histone Interaction
Weak Histone Interaction
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Histone Acetylation & Phosphorylation
Histone Acetylation & Phosphorylation
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Chromatid Separation
Chromatid Separation
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Heterochromatin
Heterochromatin
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Euchromatin
Euchromatin
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Heterochromatin Characteristics
Heterochromatin Characteristics
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Euchromatin Characteristics
Euchromatin Characteristics
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Heterochromatin Staining
Heterochromatin Staining
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Euchromatin Staining
Euchromatin Staining
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Heterochromatin Sequences
Heterochromatin Sequences
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Euchromatin Sequences
Euchromatin Sequences
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Heterochromatin Replication Timing
Heterochromatin Replication Timing
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Euchromatin Replication Timing
Euchromatin Replication Timing
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Heterochromatin Methylation
Heterochromatin Methylation
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Euchromatin Methylation
Euchromatin Methylation
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Heterochromatin Recombination
Heterochromatin Recombination
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Euchromatin Activity
Euchromatin Activity
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Histone Modification Impact
Histone Modification Impact
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Chromatin State Factors
Chromatin State Factors
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Histone Code
Histone Code
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Histone Modification Effects
Histone Modification Effects
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Histone Tail Modification
Histone Tail Modification
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Acetylation vs. Methylation
Acetylation vs. Methylation
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Methylation and Heterochromatin
Methylation and Heterochromatin
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Heterochromatin Formation
Heterochromatin Formation
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Telomeres
Telomeres
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Constitutive Heterochromatin
Constitutive Heterochromatin
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Position Effect
Position Effect
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Barrier Sequences
Barrier Sequences
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Facultative Heterochromatin
Facultative Heterochromatin
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Barr Body
Barr Body
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X-chromosome Inactivation
X-chromosome Inactivation
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Lyon Hypothesis
Lyon Hypothesis
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X Chromosome Reactivation
X Chromosome Reactivation
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Random X-inactivation
Random X-inactivation
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Stable X-inactivation
Stable X-inactivation
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Genetic Mosaics
Genetic Mosaics
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X-linked Coat Color Genes
X-linked Coat Color Genes
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Allelic Diversity
Allelic Diversity
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H1 Histone Function
H1 Histone Function
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H1 Regulation
H1 Regulation
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Histone/DNA Modifications
Histone/DNA Modifications
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Histone Deacetylation
Histone Deacetylation
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DNA Methylation
DNA Methylation
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H3 Methylation
H3 Methylation
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Chromosome Condensation
Chromosome Condensation
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Histone Acetyltransferases (HATs)
Histone Acetyltransferases (HATs)
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Histone Deacetylases (HDACs)
Histone Deacetylases (HDACs)
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Histone Methylation
Histone Methylation
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Histone Phosphorylation
Histone Phosphorylation
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HATs and Gene Activation
HATs and Gene Activation
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Acetylation and DNA Accessibility
Acetylation and DNA Accessibility
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Histone H1 Function
Histone H1 Function
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Study Notes
Heterochromatin and Euchromatin
- Session Learning Outcomes include describing chromatin packing changes during the cell cycle
- Distinguishing between heterochromatin and euchromatin
- Describing X-inactivation in mammals and explaining its function.
Chromosomes
- Interphase chromosome DNA is dispersed, allowing replication and transcription access.
- Mitotic chromosome DNA is in a condensed state
- Mitotic chromosomal state is best for delivering an intact DNA package to each new daughter cell.
- During mitosis each chromosome separates into two chromatids, with one chromatid for each daughter cell.
Chromatin Types
- Different forms of chromatin show different gene activity
Heterochromatin
- Remains compacted during interphase
- Stains darkly
- Non-active chromatin
Euchromatin
- Returns to a dispersed state after mitosis
- Stains lightly
- Less packed
- Active Chromatin.
Interphase Chromosomes
- Interphase chromosomes consist of heterochromatin and euchromatin
Heterochromatin Characteristics
- Areas are highly condensed
- Inaccessible to transcription enzymes
- Consists of silent genes
Euchromatin Characteristics
- Areas are less compacted
- Accessible to transcription enzymes, leading to more activity
Heterochromatin vs. Euchromatin
- Heterochromatin stains darkly, contains repetitive sequences, replicates later in the cell cycle, and has hypermethylated DNA
- Transcriptionally repressive, silences gene expression
- Localized to telomeres and regions flanking centromeres
Euchromatin Characteristics.
- Stains lightly, contains single copy sequences (genes), replicates early in the cell cycle during the S phase, and has hypomethylated DNA.
- Transcriptionally active and permissive for gene expression.
- Telomeres at the end of the chromosome, are heterochromatin and can't be expressed to protect the chromosome.
Heterochromatin Classes
- Heterochromatin is divided into two classes based on whether it is permanently or transiently compacted.
Facultative Heterochromatin
- Sometimes active and sometimes inactive
- Active in some cells, inactive in others
- Specifically inactivated during certain phases of an organism's life or in certain types of differentiated cells.
Constitutive Heterochromatin
- Always stays condensed in all cells
- Permanently silenced DNA
- Examples Telomeres and regions flanking centromeres
Constitutive Heterochromatin Details
- Most common in mammalian cells in regions flanking centromeres
- Found in a few other sites, such as the Y chromosome distal arm in males
Constitutive Heterochromatin Plants
- Found in many plants, telomeres consist of blocks of constitutive heterochromatin
Constitutive Heterochromatin Sequences
- Consists primarily of repeated DNA sequences with relatively few genes
Active Genes and Heterochromatin
- Active genes move to a site adjacent to constitutive heterochromatin , change position via transposition or translocation and become transcriptionally silenced, this is a position effect
- There may be components whose influence spreads, affecting nearby genes.
- Specialized barrier sequences block the spread of heterochromatin along a chromosome.
White Gene Example
- White gene at a normal location gives red eye cells, and has a barrier of heterochromatin
Barrier Function
- Separates heterochromatin from euchromatin
Rare Chromosome Inversion
- The gene is now close to heterochromatin without a barrier, so heterochromatin affects and silences the gene, resulting in white eye color.
- The presence of the barrier prevents the effect of heterochromatin on the euchromatin
Yeast Cells
- Wild type yeast cells will form white colonies
Ade2 Gene
- At the normal telomere location allows yeast cells to produces a white colong
Ade2 at Telomere
- The cell will express if normal
Ade2 moved near telomere
- Results in a non-functioning gene and a mutated red colored colony develops
- The change in color indicates silencing of the gene expression
Facultative Heterochromatin Definition
- Example: X chromosome in mammals, where cells can be active or incative
Female/Male Cells
- Female cells have two X chromosomes
- Male cells have one X chromsome & one Y chromosome
Copies of Genes
- Females have two copies of most genes on the X
- Males have one copy on the X
Transcriptionally Active
- Only one X is transcriptionally active
Barr Body
- The second X condenses as a heterochromatic clump
- The barr body ensures that cells of both males and females have the same number of active X chromosomes.
Barr Body Production
- Cells synthesize equivalent amounts of products encoded by X-​linked genes. Thus, the difference in gene dosage does not change the phenotype/ health of the organism
X Chromosome Inactivation
- Lyon hypothesis describes heterochromatization of X chromosomes in female mammals occurs during early embryonic development.
- This results inactivation of genes on that chromosome
Heterochromatized X Activation
- Heterochromatized X chromosome is reactivated in female germ cells before meiosis
Oocytes
- All gametes get a euchromatic X chromosome
Lyon Hypothesis
- Inactivation of the X chromosome happens in early embryo in a cell
- ither the maternally or paternally derived X chromosome can be inactivated at random in any cell
- Once an X chromosome inactivates it's the same down the chain
Mosaics Results
- Can lead to genetic mosaics
Alleles -X Chromosomes
- Patrernal and material X chromosomes may have different alleles for the same trait, genes encode pigments
Mammilian
- Adult females are genetic messics can have different alleles that function in different body systems
Cats/Orange
- The pigment coat color genes are tied in to the X sex chromosome- black cells in this region have the chromosome maternally
- They will not have skin color in the same ways, you see the same
- Males don't have skin like this, its one or the other for orange or black
- X-linked pigment genes in domestic felines are called calico- pigment genes aren't on humans
- no calico womem
The Histone Code
- Interaction between hystone and DNA
- Tails subject to transcriptional changes
- Generate specific emzymes from amino acid acid residues
- Acetylated and phosphoralated = binding of DNA. Also modify tails
Chromatin Functions
- State, modification, and activity depends on the histone tails
- Tail core modifications have the properties of governing characteristics
Interrelated Chromatin
- Compactions which show regions of heterochromatin.
- Likliehood of transcribed gene depends on this
Lysine
- Chemical modification can change the shape of the structure
Gene Expression
- Methyl/acetyl can alter shape of express genes.
Histone Deacetylase
- It remove actly group
Histone Methylase
- Adds methyl group to amino acid to create
Heteroshromatin silencing
- Will transfer ethy groups onto a new nucleosides, protein H1 binds to get histone
HTA Regulatory Details
- Covalent modification of histome tails
- Histome Transferance, Aceyl
- Can be modified ny Acetylation etc
Modif Stat Details
- Depends on if its phosphorylated and how
- Histone- the way that can translate modifications
Transcription Process
- Modification of histome and regulation. Modification activates
- Will transcription of the gene and binding.
H1 Compaction
- The way histone modifies DNA
- Binds inhibits new transcription
- Phosphoralation by N tail
- This causes new MRNA
Histones Code
- Direct to DNA and modification happens
- Translation breaks them down near the centrometer
- The the gene will express new MRNA
Summary
- Chromosomes are decondensed during interphase and visual
- expression and loop condensation
- Can catagorize hetero and eu
- Is divided where it's innactive
- This changes activity of genes
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Description
Explore X-linked genes in cats and humans. Learn how histone modifications like acetylation and phosphorylation affect DNA binding and gene expression. Understand the vital roles of histone N-terminal tails and histone deacetylases.
