The nucleus Flashcards
What is the nucleus?
The organelle that defines the eukaryotes; a membrane-bound compartment containing genetic material.
How many nuclei do most cells have?
Most cells have one nucleus.
Which cells are exceptions to the rule of having one nucleus?
Mature mammalian red blood cells and sieve tube cells in plants.
What are the main functions of the nucleus? (List them)
- Store genetic information
- Scrutiny and repair of the code
- Replicate genetic code prior to cell division
- Transcribe the genetic code into messenger RNA
- Edit messages for protein production
- Regulate message production
- Assemble ribosomal RNA and ribosomes
Why do eukaryotes have a nucleus?
To transcribe DNA to messenger RNA and translate it into proteins.
What are the points of regulation for expressing biologically active proteins in eukaryotic cells? (List them)
- Chromatin accessibility
- Gene regulation by DNA Methylation & Histone modifications
- Regulatory sequences controlling transcriptional initiation
- Nuclear receptors controlling transcription in response to cell signalling
- Transcription Factors
- Small non-Coding RNAs (siRNA, RNAi, miRNA)
- Recognition of mature mRNA
- Control by nuclear pore components
What is a genome?
All the DNA in a cell.
How many genomes can eukaryotes have?
Eukaryotes can have 2-3 genomes: nuclear genome, mitochondrial genome, plastid genome.
What is chromosomal packaging?
The process of tightly packaging DNA around histones to form nucleosomes.
What is the core structure formed by histones around which DNA is wrapped?
An octamer of H2A, H2B, H3, and H4.
What is euchromatin?
Loosely packed chromatin during interphase.
What is heterochromatin?
Highly condensed chromatin that makes it difficult for the cell to express genetic information.
What is the nucleolus?
A sub-organelle of the nucleus where genes for ribosomes are transcribed and ribosome assembly occurs.
What is the nuclear envelope?
A double membrane surrounding the nucleus that separates nucleoplasm from cytoplasm.
What is the function of nuclear pores?
Control the traffic of cell contents between the cytoplasm and the nucleus.
What is the size of nuclear pores?
Pore size is 10nm, allowing free passage of molecules less than 60 kDa.
True or False: The outer membrane of the nuclear envelope is studded with ribosomes.
True.
Fill in the blank: The basic unit of genetic information is called a _______.
[gene]
