4.1 THE FUNCTION OF THE NUCLEUS
WITHIN THE CELL
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There are 2 types of cells:

Prokaryotic: no true nucleus or membrane-bound organelles

Eukaryotic: have a true nucleus and membrane-bound organelles.

Animal and plant cells are both Eukaryotic.
(Refer to pp. 122 – 132 in BC Science 9)

Scientists use technologies, such as nanoprobes, to see the processes within cells
more clearly and to learn about how cell parts function and transmit messages to
the nucleus.
A SURVEY OF ANIMAL AND PLANT CELLS
Both plant and animal cells are equipped with many structures that allow the cell to perform a variety
of functions.
COMPARING PLANTS AND ANIMAL CELLS
Both
Plant Cell
Animal Cell
PLANT CEL
THE NUCLEUS: CONTROL CENTRE OF THE CELL
The nucleus contains DNA.

DNA is the molecule has the master set of instructions for: what a cell will produce, how it
will function, what it will become and when it will die.
DNA carries the master set of instructions for cell function

Instructions in the nucleus are carried in long, two-stranded molecules called
deoxyribonucleic acid (DNA).

DNA looks like a twisted ladder - two strands wrap around each other in a spiral shape.

The sides of the DNA ladder are made of sugar and phosphate.

The steps of the ladder are made of
four nitrogenous bases:
 Adenine (A),
 Guanine (G),
 Cytosine (C), and
 Thymine (T).
The arrangement of bases in DNA directs all cell activities

Everything that occurs within a cell is the result of how bases on the DNA molecule are arranged (the
DNA Message).

The bases join in a specific way:

A always joins with T

C always joins with G

the order and number of bases can vary greatly within the DNA molecule.

In humans, a single DNA molecule can be several million base pairs in length.
DNA is stored in chromatin

chromatin: a substance within the nucleus that contains DNA and Proteins


Within each strand of chromatin is 1 molecule of DNA.
When a cell is growing, the DNA is uncoiled and helps in the manufacture of proteins the cell
requires.

When a eukaryotic cell is ready to divide, chromatin coils tightly into X-shaped Chromosomes.

chromosome: a thread-like structure in a cell that carries genes (Coiled and folded
DNA)
Every organism has a specific number of chromosomes

Chromosomes in the nucleus are found in pairs.

Most human cells have 46 chromosomes arranged in 23 pairs
 The 23rd pair determines sex:

XX for females and,

XY for males
Genes are found on chromosomes

Gene: small segments of DNA located on a chromosome

Genes store the information needed to produce proteins.

Arrangement of bases in a gene will usually code to produce a
specific protein.

Each chromosome can carry thousands of genes, which contain the
information to make thousands of proteins.
Proteins determine what body cells will become & how they will function

All your body cells have the same genes (same amount of genetic information in the 46
chromosomes), but only specific genes are “read” in each cell to produce specific proteins.
 This produces specialized cells.

Specialized cells  tissues  organs

Two types of specialized proteins:
1. enzymes: proteins that help speed up chemical ractions within cells
Ex. digestive enzymes like pepsin.
2. hormones: proteins that carry messages to control cellular activities
Ex. hormones for growth
HOW PROTEINS ARE PRODUCED
Protein production in the cell involves several important steps (p. 131):
1. The nucleus receives a chemical signal to make a specific
protein.
2. The DNA message for the protein is copied into a small
molecule called RNA
3. RNA leaves the nucleus through a nuclear pore.
4. The RNA message is delivered to a ribosome, the ribosome
makes the protein.
5. The manufactured protein enters the Endoplasmic Reticulum
(ER).
6. A vesicle forms at the end of the ER, and carries the protein to
the Golgi body.
7. The Golgi body repackages the protein for transport out of the
cell.
8.
A vesicle forms off the end of the Golgi body to carry the
protein to the cell membrane.
9.
The vesicle attaches to the cell membrane, and its protein
contents are released out of the cell.
A NEW TASK FOR SCIENTISTS

Scientists used to think that one gene coded for one protein.

But, there are at least 90,000 different proteins in the human genome, but only 25,000 genes in the
human body.

Scientists are currently researching how one gene can code for more than one protein?