Cell Reproduction

Cell Division All cells are derived from pre-existing cells New cells are produced for growth and to replace damaged or old cells Differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals)

Keeping Cells Identical The instructions for making cell parts are encoded in the DNA, so each new cell must get a complete set of the DNA molecules

Two new, identical DNA strands DNA Replication DNA must be copied or replicated before cell division Each new cell will then have an identical copy of the DNA Original DNA strand Two new, identical DNA strands

Identical Daughter Cells Two identical daughter cells Parent Cell

Chromosomes

Chromosome Structure The structure of chromosomes in eukaryotic cells and prokaryotic cells is different.

Recalling Eukaryotes and Prokaryotes What is a eukaryotic cell? A “true nucleus” Membrane bound organelles Found in multicellular organisms

Recalling Eukaryotes and Prokaryotes What is a prokaryote? No membrane bound nucleus. Lacks the presence of other organelles. Unicellular organisms.

Eukaryotic Chromosomes Each chromosome is composed of a single, tightly coiled DNA molecule Chromosomes can’t be seen when cells aren’t dividing and are called chromatin

Eukaryotic Cell Chromosome Rod shaped structures. DNA is tightly coiled and compacted. Consists of a single DNA molecule wrapped around proteins called histones. Proteins involved in controlling activities of specific regions in the DNA are nonhistone proteins.

Compacting DNA into Chromosomes DNA is tightly coiled around proteins called histones

Eukaryotic Chromosomes All eukaryotic cells store genetic information in chromosomes Most eukaryotes have between 10 and 50 chromosomes in their body cells Human body cells have 46 chromosomes or 23 homologous pairs The characteristic number is different for different organisms.

Chromosomes Consist of two identical halves. Each half is called a chromatid. Chromatids are formed as the DNA makes a copy of itself before division. Chromatids are joined together at the centromere. The centromere holds the chromosomes together until division.

Chromosomes in Dividing Cells Duplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids

Prokaryotic Chromosomes Much simpler than eukaryotic chromosomes. Most cell consist of only 1 chromosome attached to the inside of the cell membrane. Circular DNA molecule associated with proteins.

Prokaryotic Chromosome The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane

Autosomes vs Sex Chromosomes Sex chromosomes are chromosomes that determine the sex of an organism and may also carry additional genes. In humans, sex chromosomes are either x or y. Females have 2 X chromosomes while males have an X and a Y.

Autosomes vs Sex Chromosomes The remaining chromosomes are called autosomes. Humans have 44 autosomes and 2 sex chromosomes.

Chromosomes Every cell of an organism produced by sexual reproduction has 2 copies of each autosome. One copy of each autosome from each parent. The two copies are called homologous pairs. Each chromosome in the pair contains genes for a specific trait.

Karyotype A picture of the chromosomes from a human cell arranged in pairs by size First 22 pairs are called autosomes Last pair are the sex chromosomes XX female or XY male

The Y Chromosome Decides Boy or Girl? The Y Chromosome Decides Y - Chromosome X - Chromosome

Diploid and Haploid Cells Cells having two sets of chromosomes are called diploid. Cells having one set of chromosomes are called haploid.

Diploid Cells Diploid cells have both chromosomes for each homologous pair. They have 2 sex chromosomes in humans and many others with sex chromosomes. All normal cells (except reproductive cells) are diploid. The diploid number is commonly abbreviated as 2n.(in humans -46)

Haploid Cells Human sperm cells and egg cells are called haploid cells (or 1n). Cells that contain only one set of chromosomes. When a sperm cell (1n) and an egg cell (1n) combine to create the first cell of a new organism, the new cell will be diploid.