(41-44) Nucleus

Nuclear envelope

double-lipid bilayer of the nucleus. The outer bilayer is contiguous with the inner bilayer (4 monolayers).

Perinuclear space

20-40 nm region between the two lipid bilayers that compose the nuclear envelope

There may be — integrated into the outer monolayer of the nuclear envelope which allows for some —

ribosomes; protein synthesis

The nucleus is shaped like a — in order to maximize — and minimize —

oval/sphere; volume; SA

nucleoplasm

gel-like substance within the cell nucleus that surrounds the chromatin and other nuclear components

Nuclear pores

regions of the nuclear envelope through which molecules may move in or out of the nucleus. Around 80 nm in diameter. Referred to as a nuclear pore complex when associated with proteins

Nuclear pore complex

a nuclear pore which contains two protein rings with a series of proteins that face inwards and small fibrous proteins that extend from the rings. The innermost portion of the protein within the pore is about 9 nm in diameter.

The hole of a nuclear pore is — nm in diameter whereas the hole in a nuclear pore complex is – nm in diameter

80; 9

Molecules which must pass through a nuclear pore complex must have what?

a tag that interacts with the fibrous proteins of the complex

Of the following molecules, which ones would NOT contain a tag allowing for transport through a nuclear pore complex; Ribosomal subunits, pyruvate kinase, RNA polymerase, or histones

pyruvate kinase ( made in the cytoplasm, functions in the cytoplasm, no need to go to nucleus)

The typical nucleus has — to — pore complexes that are (evenly or unevenly) distributed over the surface of the nucleus

3000 to 4000; evenly

Annulate lamellae

region of the nuclear envelope where a large number of nonfunctional nuclear pore complexes are stored until they are needed

Nuclear lamina (structure)

thick (50-80 nm) layer of protein associated with the nucleoplasm side of the nuclear envelope. Composed of strongly positively lamin charged proteins. The proteins form alpha helices suspended from protein receptors attached to the inner membrane of the nuclear envelope. There are some proteins suspended horizontally from the proteins forming a crosshatch.

Nuclear lamina function

Helps give the nucleus its spherical shape to maximize volume. Holds nuclear pores in place. Binds and organizes heterochromatin.

Three lamin proteins that make up the lamina

A,B, and C

The nuclear lamina is — to — nm in thickness

50 to 80 nm

Charge of lamin proteins

strongly positive

The — charge of lamin proteins allows it to bond with — charged molecules like —

positive; negative; DNA/chromatin

Nucleolus

site of large rRNA synthesis. Composed of a fibrillar and granular region

Fibrillar region

innermost region of nucleolus. Area with extremely high rRNA production. Specifically responsible for large rRNA production.

Granular region

outermost region of the nucleolus. “Assembly line”. Where the 60s and 40s subunits are synthesized

Draw and label a basic nucleus

RNPs

ribonucleoproteins (RNA bound to a protein). May appear as small granules in the nucleoplasm.

Main function of the nucleus

regulation of transcription

T/f the genetic material of all cells in an organism is the same

true

There is no difference in the production of about — to — percent of proteins between all cells in an organism

80 to 90

There are about — to — different proteins in a typical human cell

20,000 to 25,000

When is the best time to regulate protein synthesis in the nucleus? why?

transcription; no energy is wasted on an unneeded protein if it is never transcribed

Lac operon

group of genes in prokaryotes responsible for metabolism of lactose. Has a repressor constantly bound to the promoter until allolactose binds to it and allows for transcription.

Lactose

disaccharide that may be used as a source of energy in cells. Brought into cells through specific transporters. Proteins produced by the lac operon are responsible for its metabolism.

Allolactose

isomer of lactose. In equilibrium with lactose in the cell, and found in much lesser proportion than lactose. Acts as the signal that binds to the repressor protein on the promoter of the lac operon and causes it to remove itself.

Repressor protein

binds to the promoter of a gene in order to block transcription. Seen in negative gene regulation

t/f the lac operon continues to be transcribed when all the lactose in a cell has been metabolized (explain answer)

false. No allolactose will be present to remove the repressor on the promoter of the operon, therefore no transcription will take place.

One way gene transcription may be regulated (as seen in the lac operon) is for a — signal which effects the — of a gene and causes it to be —

environmental; promoter; transcribed

Negative gene regulation

when a protein (a repressor) must be removed from the promoter of a gene in order for the gene to be transcribed. (example-> lac operon)

Positive gene regulation

seen in most eukaryotic cells. A protein (transcription factors) must bind to the promoter to stimulate RNA polymerase to transcribe the gene

In eukaryotes most gene regulation is (positive or negative) gene regulation

positive

t/f one protein may act as a negative regulator on some gene or as a positive one on others

true

Turning on multiple genes at once is particularly importance in —

development of a zygote

Master gene regulation

accomplished via a master regulatory gene protein. When a protein regulates the transcription of multiple genes at once.

Ways a master gene protein may turn on multiple genes

it may bind as a transcription factor to multiple genes. May bind to heterochromatin to cause it to decondense into euchromatin (selective decondensation).

Androgen receptor

considered a master regulatory protein in males. Initiates all the secondary sex characteristics of male anatomy

Selective decondensation

process by which a portion of genes associated with nucleosomes are loosened from the nucleosome in order for transcription to occur

Processes by which selective decondensation may occur

H1 phosphorylation, Histone acetylation, histone replacement, polyamines

H1 phosphorylation

process by which phosphates are added to the h1 histone protein causing it to become more negative in charge and loosen its connection with DNA (recall that the H1 histone is associated with linker DNA)

Histone acetylation

process by which acetates are added to histone proteins (H2A,H2B, H3, or H4) which reduce the positive charge of the protein (acetates are C-C groups which are neutral) . this less positive charge causes its connection with DNA to loosen

Histone replacement

the switching of various histones with other histones. May allow for decondensation if the replacement histone has a less positive charge

Polyamines

short hydrocarbon with two primary amines and maybe secondary amines within the chain. interacts directly with DNA. may align with the helices and neutralize the negative charge of the DNA phosphate groups. This causes it loosen off of the positively charged histones.

Putrescine

polyamine with a 4 carbon chain two primary amines. originally found in cadavers

Polytene chromosomes

giant chromosomes formed in fruit fly salivary glands. Seen as the DNA replicates while the cell does not divide. Creates these huge bundles of chromatids

Chromosome puff

regions of polytene chromosomes that look “fuzzy”. Appears and disappears constantly on the polytene chromosomes. Represents areas of selective decondensation.

The most decondensation seen on one chromosome was about – % of the chromosome being decondensed

7