The Cell Many living things are unicellular – they consist of a single cell.

Other living things are multicellular, consisting of many cells – many trillions of cells in the case of human adult. The cell is in several senses the basic unit of a living organism. There are more than 200 distinct kinds of cells in the human body. All living things are composed of cells, and all cells arise from preexisting cells.

Plasma membrane Every living cell is surrounded by a plasma membrane that regulates the entry and exit of molecules and ions and that contains receptors for various external signals.

Eukaryotic cell structure Compared with a prokaryotic cell, a Eukaryotic cell is full of

membranous structures. Unlike a prokaryotic cell, a Eukaryotic cell contains a nucleus and numerous membrane – bounded organelles. But , like a prokaryotic cell, it contains many ribosomes for protein assembly.

Prokaryotic cell (Bacteria ) Eukaryotic cell (Animal cell )

Plasma membrane

Organelles Organelles are subcellular structures with specialized functions.

Among the kinds of organelles are the ribosomes, the mitochondria,.. many organelles are membrane – bounded, but ribosomes are not.

Nucleus The nucleus is the information center of a eukaryotic cell. A

double-membraned nuclear envelope bounds the nucleus with its enclosed, linear chromosomes. The nucleoplasm is the fluid material within the nucleus, suspending the chromosomes and nucleoli.

Nuclear envelope The nucleus of a cell (a Eukaryotic cell, that is … recall that

prokaryotic cells lack nuclei) is surrounded by a double membrane, the nuclear envelope is perforated by nuclear pores. The nuclear envelope breaks down at the onset of prometaphase in mitosis or meiosis, and it forms again during telophase.

Nucleus Nucleus

Nuclear envelope

Nuclear lamina In Eukaryotic a nuclear lamina lines the inside of the inner

membrane of the nuclear envelope. Intermediate filaments, woven together, constitute the nuclear lamina. These intermediate filaments are made of proteins called nuclear lamins. Breakdown of the nuclear lamina precedes the disappearance of the nuclear envelope at the start of prometaphase.

Nuclear poreThe nuclear envelope is perforated by nuclear pore … channels

that allow the passage of certain molecules between nucleus and cytoplasm. Each pore is part of a nuclear pore complex consisting of over 100 different proteins.

Nuclear lamina

Nuclear pores

Chromatin Chromatin is the DNA-protein complex found in eukaryotic chromosomes. It is replicated during the S phase of the cell cycle.

Chromosome Chromosome contains all or almost all the hereditary material of a cell. A single Chromosome contains a large number of genes, each with its own locus (place) on the Chromosome. A Chromosome consists of a large molecule of DNA and a number of protein molecules. Chromosome change dramatically in structure during the cell cycle.

Nucleolus A Nucleolus is a small, generally spherical body found within the nucleus of eukaryotic cells. Transcription of ribosomal RNA (rRNA) takes place in the nucleoli, as does the assembly of ribosomal subunits. The nucleoli contain ribosomal RNA (rRNA) and many copies of the genes that encode rRNA. The number of nucleoli in a nucleus is characteristic of a species, one is the most common number.

Chromosome

Nucleolus

Nucleoplasm Nucleoplasm is the fluid material within the nucleus. Chromosomes, nucleoli, and other particulate components of the nucleus, as well as the nuclear envelope, are distinct from the Nucleoplasm.