Eukaryotic Cell Structure

Ribosome

Ribosomes are composed of ribosomal RNA (rRNA) and protein. Composed of two subunits with densities of 50S and 30S. ("S" refers to a unit of density called the Svedberg unit.) The two subunits combine during protein synthesis to form a complete 70S ribosome about 25nm in diameter. A typical bacterium may have as many as 15,000 ribosomes.
Organelles Used in Bacterial Photosynthesis

There are three major groups of photosynthetic bacteria: cyanobacteria, purple bacteria, and green bacteria. The cyanobacteria carry out oxygenic photosynthesis, that is, they use water as an electron donor and generate oxygen during photosynthesis.The photosynthetic system is located in an extensive thylakoid membrane system that is lined with particles called phycobilisomes.

植物细胞的基本构造英文回答：Plant Cell Basic Structure.Plant cells are eukaryotic cells, meaning they have a true nucleus and other membrane-bound organelles. They are also unique in their possession of a cell wall, chloroplasts, and a large central vacuole.Cell Wall.The cell wall is a rigid structure that surrounds the cell membrane and provides support and protection. It is composed of cellulose, hemicellulose, and pectin. The cell wall also contains pores that allow water and nutrients to enter and exit the cell.Cell Membrane.The cell membrane is a thin, flexible layer that surrounds the cytoplasm. It controls the movement of substances into and out of the cell. The cell membrane is composed of a phospholipid bilayer with embedded proteins.Cytoplasm.The cytoplasm is the gel-like substance that fills the cell. It contains all of the cell's organelles, including the nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, and chloroplasts.Nucleus.The nucleus is a membrane-bound organelle that contains the cell's DNA. DNA is the genetic material that controls all of the cell's activities. The nucleus also contains the nucleolus, which is a small structure that produces ribosomes.Endoplasmic Reticulum.The endoplasmic reticulum is a network of membranesthat folds and transports proteins. The rough endoplasmic reticulum is studded with ribosomes, which are small structures that assemble proteins. The smooth endoplasmic reticulum is involved in the synthesis of lipids and carbohydrates.Golgi Apparatus.The Golgi apparatus is a stack of flattened membranes that modifies and packages proteins. Proteins are transported from the endoplasmic reticulum to the Golgi apparatus, where they are sorted and packaged into vesicles. The vesicles then transport the proteins to their final destination.Mitochondria.Mitochondria are small, bean-shaped organelles that produce energy for the cell. They are often called the "powerhouses of the cell." Mitochondria contain their own DNA, which is different from the DNA in the nucleus.Chloroplasts.Chloroplasts are green organelles that contain chlorophyll, a pigment that absorbs light energy from the sun. Chloroplasts use the light energy to convert carbon dioxide and water into glucose, a sugar molecule that provides energy for the cell.Vacuole.The vacuole is a large, membrane-bound organelle that stores water, salts, and other molecules. The vacuole also helps to maintain the cell's shape and turgor pressure.中文回答：植物细胞的基本结构。

DNA molecules must be compacted 104-fold
The importance of packing of DNA into chromosomes
Chromosome is a compact form of the DNA that readily fits inside the cell [?]
A Severe Problem of Packaging
1. Largest human chromosome: ~3 x 108 bp How long is it?
3 x 108 bp x 3.4 Å/bp = 10 x 104um! 2. A typical cell = 10 um
Conclusion: chromosome in length/size of cell
Supercoiling of the genome
supercoil of the genome
unconstrained supercoil function: pass tensile forces among loops
constrained supercoil (bind proteins) 结构域被非特异结合蛋白如HU和H-NS等类 组蛋白缠绕，使一半超螺旋被束缚。
146bp的DNA片段和H2A、 H2B、H3和H4各二分子组 成,这种结构称为核心颗粒.
• 核心颗粒外观呈椭圆形,颗粒直径11nm,高 5.5nm.绕颗粒的DNA长度为50nm(146bp),连 接区DNA长度为20nm(约60bp).
11nm染色质纤维
The roles of H1
1. Stabilizes the point at which DNA enters and leaves the nucleosome core. Protect the further 20bp DNA from nuclease digestion.

微生物学名词解释微生物(Microbe): 微观的生物机体。

(细小的肉眼看不见的生物)微生物(Microorgamism): 微观的生命形式。

微生物学(microbiology)：研究微生物生命活动的科学。

微米(Micrometer): 一种测量单位：1/1,000mm,缩写为um。

原核微生物(prokaryotic microbe)：指核质和细胞质之间不存在明显核膜，其染色体由单一核酸组成的一类微生物。

原核细胞型微生物(procaryotic cell microbe):指没有真正细胞核（即核质和细胞质之间没有明显核膜）的细胞型微生物。

真核细胞型微生物(eukaryotic cell microbe):指具有真正细胞核（即核质和细胞质之间存在明显核膜）的细胞型微生物。

真菌(fungi)：有真正细胞核，没有叶绿素的生物，它们一般都能进行有性和无性繁殖，能产生孢子，它们的营养体通常是丝状的且有分枝结构，具有甲壳质和纤维质的细胞壁,并且常常是进行吸收营养的生物。

霉菌(Mold): 具有丝状结构特征的真菌。

细菌(bacterium)：单或多细胞的微小原核生物。

病毒(virus)：是一类没有细胞结构但有遗传复制等生命特征，主要由核酸和蛋白质组成的大分子生物。

是比细菌更小的专性细胞内寄生的微生物，大多数能通过细菌过滤器。

放线菌(actionomycetes）：一目形成真的菌丝成分枝丝状体的细菌。

蓝细菌(cyanobacterium)：是光合微生物，蓝细菌是能进行光合作用的原核微生物。

原生生物(protistan)：指比较简单的具有真核的生物。

原生动物(protozoa)：单细胞的原生生物。

免疫学(immunology)：研究利用预防接种法治疗疾病的科学。

立克次氏体(Richettsia)：节肢动物专性细胞内寄生物，它的许多类型对人和其它动物是致病的微生物。

感染(Infection): 宿主由于微生物生长的病理学状况。