The Nucleus (all you need to know for OCR A cells exchange and transport)

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The Nucleus
Properties of the Nucleus
Houses almost all of the cell's genetic material
It is also the largest organelle and is surrounded by a nuclear envelope,
which is made up of 2 membranes with fluid between them.
Nuclei contain pores which go right through envelope to allow movement between the cytoplasm and these pores
large enough for large molecules to pass through.
The Nucleus coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and
reproduction (cell division).
Not all cells have a nucleus. Biology breaks cell types into EUKARYOTIC (those with a defined nucleus) and
PROKARYOTIC (those with no defined nucleus).
The Nucleolus
The Nucleolus is a membraneless organelle within the nucleus that makes
ribosomes and RNA, the cell's proteinproducing structures.
If seen through a microscope it seems like a large dark "spot" within the
nucleus.
A nucleus may contain up to four nucleoli, but within each species the number of nucleoli is fixed.
After mitosis, the nucleolus is formed when chromosomes are brought together into "nucleolar" organizing regions.
The Nuclear Envelope
The nuclear envelope is a doublelayered membrane that encloses the
contents of the nucleus during most of the cell's lifecycle.
There is space between each "layer" called the perinuclear space and
appears to connect with the rough endoplasmic reticulum.
Contains small holes known as pores which regulate which molecules can
enter the nucleus region from the cytoplasm.
Along the inner surface of the nucleus, one of these networks is organized into a special meshlike lining called the
nuclear lamina, which binds to chromatin, integral membrane proteins, and other nuclear components.
Nuclear Pores
The nuclear envelope contains holes called nuclear pores.
These pores regulate the passage of molecules between the nucleus
,cytoplasm, permitting some to pass through the membrane, but not
others.
Building blocks for making DNA and RNA are allowed into the
nucleus as well as molecules that provide the energy for constructing
genetic material.

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Chromatin
Packed inside the nucleus of every human cell is nearly 6 feet of
DNA, which is divided into 46 individual molecules, one for each
chromosome and each about 1.5 inches long.
For DNA to function, it can't be crammed into the nucleus like a
ball of string.
Instead, it is combined with proteins and organized into a precise, compact structure, a dense stringlike fibre called
CHROMATIN.…read more

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