Science Notes (textbook pgs. 120-132)

By: Noahm Rozen

CELLS AND ORGANELLES

PLANT CELLS:

Cell wall – a tough rigid structure surrounding the cell membrane. Provides support for the plant cell.

Chloroplast – an organelle that traps energy from the sun and uses it as energy for the plant cells.

Vesicles – membrane covered sacs that form off the ends of the endoplasmic reticulum. Vesicles transport new proteins to the Golgi

Body for further processing and export out of the cell.

BOTH (animal and plant cells):

Cell membrane – a thin covering that goes over a cell, controls what goes in and out of the cell

Cytoplasm – a jelly-like substance that contains the organelles and other life-supporting materials such as water and sugar.

Mitochondria (p)/mitochondrion (s) – organelles that are specialized to provide energy for cells by engaging sugar called glucose into usable energy.

Ribosomes – are small organelles that do not have a membrane. Some float in cytoplasm, others are attached to the endoplasmic reticulum.

Proteins – are essential materials required for cells to carry out the activities necessary for survival.

Endoplasmic reticulum – a network of membrane-covered channels within a cell. The organelle acts as a transport system for materials made in the cell.

Golgi Body – a specialized organelle that sorts and packages proteins for transport.

Vacuole – a membrane covered storage within cells. Plant cells often contain small vacuoles to store starch and a large one to store water. Some animal cells have vacuoles.

NUCLEUS (plural nuclei) – the organelle that controls all the activities of cell parts described above.

THE NUCLEUS:

Nuclear membrane – surrounds the nucleus, is similar to the structure of the cell membrane. The nuclear membrane protects the contents of a nucleus.

Nucleolus – a membrane free organelle that floats in the interior of the nucleus. The function of the nucleolus is to make ribosomes.

Nuclear pores – openings in the nuclear membrane that allow only certain materials into and out of the nucleus. Ribosomes made in the nucleus will leave through the pores and go to the cytoplasm or endoplasmic reticulum.

DEOXYRIBONUCLEIC ACID (DNA)

The instructions in the nucleus are carried in long two-stranded molecules called DNA. It looks like a twisted ladder (as seen above). Scientists call it the double helix.

·      The sides of the DNA ladder are made of sugar

·      The “steps” of the ladder are made of four nitrogen bases, which are represented by letters.

·      The letters are: A (adenine), G (guanine), C (cytosine), and T (thymine)

Everything that occurs within a cell is the result of how the bases on the DNA molecule are arranged. Bases in a DNA molecule always join in a specific way:

·      A always joins with T

·      G always joins with C

The order and number of these bases can vary within the DNA molecule.

In humans, single DNA molecule can be several million base pairs in length.

DNA IS STORED IN CHROMATIN:

Most of the time, DNA exists in the nucleus as chromatin

Chromatin – a substance that contains DNA and proteins.

Within each strand of chromatin is one molecule of DNA. When a cell is growing, the DNA is uncoiled and helps in the distribution of proteins the cell requires.

EVERY ORGANISM HAS A CERTAIN NUMBER OF CHROMOSOMES:

Most human cells have 46 chromosomes arranged in 23 pairs, including one pair that helps determine gender. For males the 23^rd pair is the XY pair, and for females it’s the XX pair.

GENES ARE FOUND ON CHROMOSOMES:

Genes – small segments of DNA located at specific places on a chromosome.