THE CELL Flashcards
Structure of the Nucleus
Appears as a large rounded or oval structure near the cell center.
What is the function of the Nuclear Envelope?
Forms a selectively permeable barrier between the nuclear and cytoplasmic compartments.
What is the structure of the Nuclear Envelope
Composed of two concentric membranes separated by a perinuclear space.
The outer nuclear membrane is continous with the?
Continuous with the Rough Endoplasmic Reticulum (RER).
The inner nuclear membrane is associated with?
Associated with a meshwork of proteins called the nuclear lamina.
What are Nuclear Pore Complexes?
They bridge the inner and outer nuclear membranes.
The Chromatin consists of?
Consists of DNA and associated proteins in an uncoiled state.
2 TYPES OF CHROMATINS
- HETEROCHROMATIN
- EUCHROMATIN
What is a Heterochromatin?
Electron-dense material, basophilic clumps
What is a Euchromatin made up of?
Finely dispersed granular material
What Chromatin is Present in females yet absent in males?
Barr Body (Sex Chromatin)
DNA in chromatin is extensively packaged by associating with basic proteins called?
histones
What do histones provide for a chromosome?
Histones provides structural support for a chromosome
What is a chromatid?
Each long DNA double helix with its associated proteins
After DNA replication, two chromatids held together by complexes of cohesin proteins make up each ____?
chromosome
Fill in the blanks: X and Y chromosomes determine _____, while autosomes are _____ pairs.
X and Y chromosomes: sex
Autosomes: homologous pairs
Difference Between Chromosome and Chromatid:
Chromosome: a DNA molecule with part or all of the genetic material (genome) of an organism
Chromatid: one copy of a newly copied chromosome which is still joined to the original chromosome by a single centromere
Traits of a Euchromatin: (11)
- Transcriptionally active
- DNA is loosely packed
- Actively present in prokaryotic and eukaryotic genome
- Genetically active
- Present at the inner side of the nucleus
- Stained lighter
- Early replicative
- Aren’t sticky
- Allow genes to form proteins
- Low genetic density
- Consists of 2 to 3% of the genome
Traits of a Heterochromatin: (11)
- Transcriptionally inactive
- DNA is highly packed
- Only present in eukaryotic genome
- Genetically inactive
- Present at nucleus periphery
- Stained dark
- Late replicative
- Are usually sticky
- Regulates genetic integrity and controls gene expression
- High genetic density
- Consists of 97 to 98% of the genome
X and Y sex chromosomes contain genes that determine what?
whether an individual will develop as a female or a male.
In addition to the pair of sex chromosomes, cells contain pairs of _____?
autosomes
Each of these pairs of chromosomes contains one chromosome originally derived from the mother and one derived from the father. The members of each chromosomal pair are called _____?
Homologous
Why are cells of most tissues (somatic cells) considered diploid?
because they contain pairs of chromosomes.
Sperm cells and mature oocytes are haploids because?
they contain half the diploid number of chromosomes, each pair having been separated during meiosis
Characteristics of a Haploid (n) [2]
• One copy of each chromosome
• Three non-homologous chromosomes
What are two characteristics of a Diploid (2n)?
• Two copies of each chromosome
• Three pairs of homologous chromosomes (of maternal and paternal origin)
What is the function of the nucleolus?
Involved in the synthesis of ribosomal RNA (rRNA) and the assembly of ribosome subunits.
Describe the structure of a nucleolus
Spherical, highly basophilic subdomain of nuclei.
In the Nucleolus, Intense basophilia of nucleoli is due not to heterochromatin but to the presence of?
densely concentrated ribosomal RNA
What is it called when there is a regular sequence of events that result in new cells?
The Cell Cycle
Before differentiation, most cells undergo repeated cycles of two processes:
macromolecular synthesis (growth) and division (mitosis)
Four distinct phases of the cell cycle:
▫ Mitosis
▫ G1 (the time gap between mitosis and DNA replication)
▫ S (the period of DNA synthesis)
▫ G2 (the gap between DNA duplication and the next mitosis)
Describe what is the Interphase:
It is considerably longer than the M phase and is the period during which the cell doubles in size and DNA content.
The Longest and most variable phase of the cycle
G1
G1 is the time gap between _____ and _________
Mitosis and DNA replication
G1 is also the period of?
Period of active RNA and protein synthesis, including proteins controlling progress through the cell cycle
The S phase is characterized by? (3)
- DNA replication
- histone synthesis
- beginning of centrosome duplication
The phase where Proteins are required for mitosis accumulate
G2 phase
What happens in the Go phase?
Cell cycle activities may be temporarily or permanently suspended
Entry or progression through other phase of the cycle is also monitored at specific what?
checkpoints
Checkpoints are where certain conditions must be met before?
the cell continues cycling
