Histology Chapter 3 - The Nucleus

What is the size of nuclei in active cells?

large

What are the three functions of the nucleus?

1. contains a blueprint for all cell structures and activities

2. contains the molecular machinery to replicate DNA and RNA

3. imports protein molecules needed for nuclear activity from the cytoplasm

3 main components of the nucleus:

nuclear envelope, nucleolus, chromatin

What is the nuclear envelope?

a paired membrane that regulates flow in and out of the nucleus

What occurs in the nucleolus?

site of ribosome production

What does the nucleolus look like and why?

darkly stained due to protein synthesis

DNA is coiled around proteins called _______.

histones

Nuclear lamina

intermediate filaments that provide mesh-like support to the envelope

Nuclear pore complexes (NPCs)

regulate bidirectional transport of material between the cytoplasm and the nucleus

How many pore complexes are there per nucleus?

3000 to 4000

Each NPC is made of 30 different proteins called:

nucleoporins

Verse about being knit together:

Psalm 139:13-14

What structure is this?

nuclear lamina

What structure is this?

nuclear pore complexes

Nuclear lamina contains binding sites for __________.

chromatin (mainly heterochromatin)

Is chromatin present at the NPCs?

no

What is a pyknotic nucleus?

one that is dark and shrunken, indicating irreversible cell death

Two things that can result in a pyknotic nucleus?

hypoxia and over-exercise causing a lactic acid buildup

#1 cause of cell death

hypoxia

What are the white areas of the nucleolus?

Fibrillar center (FC)

What are the dark areas of the nucleolus?

pars fibrosa

Another name for fibrillar center:

nucleolar organizer (NO)

What does the Pars Fibrosus contain?

contains the proteins fibrillarin and nucleolin

What are the bumpy/grainy parts of the nucleolus?

pars granulosa

What is in the Pars Granular?

assembled ribosome subunits

What is the closest organelle to the nucleus?

rough ER

What is ‘NO’? (it is incorrectly labeled in the image)

pars fibrosa

What is ‘PF’? (it is incorrectly labeled in the image)

pars granulosa

How do ions and small molecules pass through the nuclear pore?

passive diffusion

How to larger molecules and molecular complexes pass through nuclear pores?

NLS is needed along with Ran GDP and importins to get the cargo in; NES is needed along with Ran GTP and exportins to get cargo out

Example of an exportin:

Crm1

Proteins greater than what molecular weight require an NLS to get into the nucleus?

80 kd

What is the function of the nucleolus?

protein synthesis, especially ribosome production

What does NAC stand for?

nucleolar associated chromatin

What is NAC?

the portion of nuclear chromatin associated with the nucleolus; includes the DNA encoding the ribosomal RNA

What is attached to the nucleus at the periphery?

heterochromatin

What are the dark structures in the cell?

nucleoli

Are the nucleoli active or inactive?

active

Nucleosome

basic structural unit of chromatin and histones

What histones make up a nucleosome?

two copies of each of H2A, H2B, H3, and H4 (H1 is outside the nucleosome)

How much shorter is compacted heterochromatin than unpacked euchromatin?

40,000x

How long is the DNA in each human cell?

1.8 meters

During mitosis and meiosis chromatin is coiled by the histones into a visible structure called a _________.

chromosome

Where is condensin 1?

in the cytoplasm

Where is condensin 2?

in the nucleus

What does condensin 2 do?

helps breakdown nuclear membrane and packages DNA to chromosomes

What does condensin 1 do?

reassembled nuclear membrane after division is complete

During what two phases do condensin 1 and 2 contribute to the assembly of condensed chromosomes, in which two sister chromatids are fully resolved?

prometaphase and metaphase

What structure joins the two sister chromatids?

centromere

How many autosomes are found in most human cells?

22

The members of each chromosomal pair are called _________.

homologous

Somatic cells are _______.

diploid

How many chromosomes in gametes?

23

Cytogenetic notation of a normal human male?

46, XY

Cytogenetic notation for a normal human female?

46, XX

Cytogenetic notation for a male with Down’s Syndrome?

47,XY+21

p vs q for cytogenetic notation:

p is for short arm and q is for long arm

What drug is used to arrest cells in metaphase?

colchicine

Technique used to examine all chromosomes at once?

karyotyping

Metacentric

centromere in the center

Submetacentric

centromere position results in one short arm and one long arm

Acrocentric

centromere position results in one long arm and a short stalk with a satellite

What does q stand for as the long arm of a chromosome?

it was chosen as the next letter in the alphabet following p

Sex chromatin definition:

a mass of heterochromatin observed in female nuclei and not males

Another name for sex chromatin:

Barr Body

What is being pointed to?

Barr Body

In what WBC can we see Barr bodies clearly?

neutrophils

At what point in development can you see a distinct sex difference?

6 weeks

Four types of intersex syndromes:

1. hermaphroditism

2. female pseudohermaphroditism

3. male pseudohermaphroditism

4. Complex or Undetermined Intersex Disorders

What is hermaphroditism?

a person is born with both male and female sex organs

What is the underlying cause of hermaphroditism?

unknown

What is female pseudohermaphroditism?

chromosomes of a woman, external genitalia appears male

Another name for Female Pseudohermaphroditism?

46, XX Intersex

Another name for male pseudohermaphroditism?

46, XY Intersex

What is male pseudohermaphroditism?

chromosomes of a man, genitalia appears female

What is the cause of 46, XX Intersex?

female fetus exposed to excess male hormones before birth

What is 46, XY Intersex caused by?

male fetus exposed to female hormones before birth

What 3 things does 46, XY intersex cause?

1. problems with the testes

2. problems with testosterone formation

3. problems with using testosterone

3 disorders that fall in the complex/undetermined intersex disorder category:

45, XO

47, XXY

47, XXX

How to complex intersex disorders affect external genitalia?

no discrepancy between internal and external genitalia

2 male symptoms of complex intersex disorders:

micropenis and undescended testes

3 female symptoms of complex intersex disorders:

clitoromegaly, partial labial fusion, labial or inguinal masses

What is a common male/female symptom of complex intersex disorders?

hypospadias

What are hypospadias?

opening of the urethra at the wrong spot

Kleinfelter Syndrome

47, XXY

Incidence of Kleinfelter Syndrome

1 out of 1000

Incidence of Down’s Syndrome?

1 in 733

What are the stages of interphase?

Growth (G₁), synthesis (s), and growth (G₂)

Mitotic phase of the cell cycle includes what phases:

prophase, metaphase, anaphase, telophase, cytokinesis

What happens at G₀?

cell temporarily or permanently ceases dividing at this checkpoint

What protein (in what state) blocks cells at G₀?

unphosphorylated Rb

What happens when Rb is phosphorylated?

G₀ proceeds to S phase

What two proteins are involved in phosphorylating Rb?

Cyclin D and cdk4

When does cytokinesis begin?

end of anaphase

prophase

metaphase

anaphase

telophase

What type of microscopy is this?

fluorescent

What phase is this?

metaphase