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Flashcards in DNA packaging and the nucleus Deck (35)
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1
Q

What is histone proteins function?

A

Structural component of chromatin - packages DNA

2
Q

Why is packing DNA important?

A

Pack lots in small space and makes DNA less vulnerable

3
Q

Describe the electrostatic attractions in chromatin?

A

Histone has cationic surface (+ charged AA) attracted to -ve DNA charged phosphate groups - allow tight wrapping of DNA

4
Q

What is the structure of a histone?

A

Octamer entailing 2 sets of H2A, H2B, H3 and H4 with DNA wrapped around (nucleosome) - stabilised by H1 protein and joined by linker DNA

5
Q

Describe different levels of organisation of chromatin?

A

Bead and string model, 10nm fibre.

Fibril supercoiled. Nucleosomes are folded and stacked creating 30nm solenoid fibril
(2m DNA into 5micrometer wide nucleus)

6
Q

What bonds underpin the histone protein?

A

Hydrogen bonds between the DNA backbone and the amide group of histone proteins.

Nonpolar interactions between the histone and deoxyribose sugars on DNA.

Salt bridges and hydrogen bonds between side chains of basic amino acids (especially lysine and arginine) and phosphate oxygens on DNA.

7
Q

When does highest degree of compaction of genome occur?

A

In mitosis - not transcriptionally active

8
Q

What are the functions of nucleus?

A

Gene replication + repair

Gene transcription

Ribosome production in nucleoli

9
Q

What are nucleoli, what’s the function?

A

Dense regions of DNA, RNA and protein (nucleoprotein)

Site of ribosome production -exported via nuclear pores

10
Q

How many homolgous pairs of chromosomes does nucleus have?

A

22 (+1 pair of sex chromosomes)

11
Q

Structure of nucleus (inc size)?

A

7-8 micrometer

Nuclear envelope (defines eukaryotes)

Double membrane contains pores allow macromolecules to cross (perinuclear space in between)

Inner nuclear membrane (nuclear lamina) contains scaffold like network of protein filaments - maintain nuclear shape

12
Q

Describe how condensed DNA is in interphase, why?

A

Chromatin less compact allow enzymes to access DNA

13
Q

Describe difference between faculative and constitutive heterochromatin?

A

Constitutive heterochromatin: always condensed and inactive. Found at chromosomal centromeres and telomeres

Faculative heterochromatin: condensed but can be actively transcribed -euchromatin e.g. one X chromosome packaged as Barr body - silenced (other is packaged as euchromatin)

14
Q

Explain how mitotic and interphase chromosomes differ under light microscope?

A

Mitotic chromosomes visible but interphase ones are not

15
Q

Describe structure and appearance of euchromatin and heterochromatin?

A

Euchromatin: less comapct and stains lightly containing most active genes

Heterchromatin: chromatin more tightly packed dark staining

16
Q

What is a chromatin loop?

A

Stretches of genomic code, that lie on the same chromosome, are in closer physical proximity to each other than to the base sequence between the two points

17
Q

What is the role of chromatin loops?

A

Allows regulation

18
Q

Describe how chromosome territories are characterised?

A

Territories are determined by genomic regions, such as, the lamina-associated domains (LADs), and the topologically associating domains (TADs)

19
Q

What is involved in a LAD?

A

Anchoring specific parts of DNA to the nuclear lamina.

20
Q

What type of chromatin do lads consist of?

A

Transcriptionally silent

21
Q

What type of DNA sequence is packaged as constitutive chromatin?

A

High copy number tandem repeats: satellite repeats, mini-satellite and microsatellite repeats, and transposon repeats.

22
Q

How can facultative chromatin be silenced?

A

Histone deacetylation or Piwi-interacting RNA (piRNA) through RNAi

23
Q

What is the diameter of the DNA double helix?

A

2nm

24
Q

~ what % of the cell volume does the nucleus make up?

A

10%

25
Q

What is the role of the nuclear envelope?

A

Separates the cell’s genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm and the cytoplasm

26
Q

What is the outer nuclear membrane continuous with?

A

RER

27
Q

What is the name of the area between the inner and outer nuclear envelope?

A

Perinuclear space

28
Q

What can pass through the nuclear pore?

A

Small water-soluble molecules

29
Q

What is the role of the nucleolus?

A

Synthesis of rRNA and assemble ribosomes

30
Q

Does the nucleolus have a membrane?

A

No

31
Q

The number of helical turns per ~10 nucleotides in natural B-form DNA…

A

1

32
Q

The nitrogenous base in a nucleotide is attached to the sugar via a covalent…

A

C-N bond

33
Q

The presence of a nuclear envelope around the core genetic material defines a eukaryotic cell.

A

True

34
Q

Chromatin is composed of which macromolecules?

A

Protein, RNA and DNA

35
Q

What is DNA helical periodicity?

A

Base pairs per turn on the nucleosome

10 for DNA