Plant & Animal Cells & Descriptions of Organelles

Nucleus

• The central genetic organelle of plant and animal cells is the nucleus. It contains the genetic material necessary for reproduction and the direction of all cellular activity. DNA, or deoxyribonucleic acid, is present in elongated strands of chromatin. During cellular division, known as mitosis, the chromatins form individual coils of chromosomes. The nucleus is walled off by a double layer of membranes called the nuclear envelope. The lumen is the space between the membranes.

Genetic Organelles

• Contiguous to the outer nuclear membrane wall are systems of organelles known as the endoplasmic reticulum, or ER. In both plant and animal cells, the reticula's tubules and vesicles help manufacture and move proteins around the cell's cytoplasmic interior. Organelles called ribosomes are attached to the rough ER and synthesize proteins. Ribosomes are composed of RNA, or ribonucleic acid and are built by the cell's DNA from a template. The smooth ER stores the proteins until they are transported around the cell's interior.

Animal Cell Organelles

• Mitochondria are important organelles that serve as the power centers of animal cells. They have a smooth outer membrane with a highly convoluted inner membrane. The inner membrane's folds are called cristae and add oxygen to sugar to make ATP, or adenosine triphosphate, the cell's energy source. Microtubules and microfilaments form the cell's cytoskeleton and allow movement and locomotion. The Golgi apparatus is made of vesicles that package and transport macro-molecules of enzymes and hormones. Vacuoles digest food and excrete cellular waste.

Plant Cell Organelles

• The largest plant cell organelle is the vacuole. Much larger than in animal cells, plant cell vacuoles perform multiple functions. They store nutrients and excretory materials. Vacuoles control the turgor, or water pressure, of plant cells. The vacuoles collect water and regulate the cell's rigidity to prevent wilting. Chloroplasts use chlorophyll to produce food through the chemical process of photosynthesis. They provide the plant's green color. Peroxisome organelles convert fatty acids to sugars by the actions of oxidative enzymes.