第二章细胞基本知识概要细胞生物学

第二章细胞基本知识概要细胞生物学

第二章细胞基本知识概要

本章内容提要:

第一节细胞的基本概念

第二节非细胞形态的生命体

-------病毒及其与细胞的关系

第三节原核细胞与古核细胞

第四节真核细胞基本知识概要

第一节细胞的基本概念

What is a cell?

Cells are structural units that make up plants and animals,

also there many single cell organisms. What cells all have in

common is they are small 'sacks' composed mostly of water. The

'sacks' are made from a phospholipid bilayer. The membrane is

semi-permeable (allowing some things to pass in or out of the

cell and blocking others), there are also other methods of

transport that we will get into later.

So what is in a cell? The cell as we mentioned is a fluid like

membrane that surrounds the contents of the cell. Each

component will be discussed in more detail later.

一、细胞是生命活动的基本单位

1、一切有机体都由细胞构成，细胞是构成有机体的基本单位；

2、细胞具有独立的、有序的自控代谢体系，细胞是代谢与功能的基本单位

3、细胞是有机体生长与发育的基础

4、细胞是遗传的基本单位，细胞具有遗传的全能性

5、没有细胞就没有完整的生命

二、细胞的基本共性

1.所有的细胞表面均有由磷脂双分子层与镶嵌蛋白质构成的生物膜，即细胞膜。

2.所有的细胞都含有两种核酸:即DNA与RNA作为遗传信息复制与转录的载体。

3.作为蛋白质合成的机器─核糖体，毫无例外地存在于一切细胞内。

4.所有细胞的增殖都以一分为二的方式进行分裂。

第二节非细胞形态的生命体—病毒及其与细胞的关系

一、Basic characteristics of viruses

Simply stated, viruses are merely genetic information

surrounded by a protein coat. They may contain external

structures and a membrane. Viruses are obligate（专性的）intracellular parasites--meaning that they require host cells to

reproduce.

In the viral life cycle, a virus infects a cell, allowing the viral

genetic information to direct the synthesis of new virus particles

by the cell.

There are many kinds of viruses. Those infecting humans

include polio（脊髓灰质炎）, influenza, herpes （疱疹）, and

human immunodeficiency virus (HIV) causing AIDS.

二、viral reproduction(i.e. the course of viral infection, e.g.

HIV infection)

1、Attachment(getting in)

On the surface membrane of all living

cells are complex protein structures called

"receptors". A receptor is often compared to

a lock into which a specific key or "ligand" will fit. There are

at least two receptors on T-lymphocytes to which the human

immunodeficiency virus (HIV) sticks. The primary receptor, called

"CD4", is shown on the right in the diagram. But a second

receptor that loops through the cell membrane 7 times is critical

for infection to occur.

HIV infection of a lymphocyte requires attachment of the

virus to the cell membrane through both of these "ligand-receptor" links. In cells whose "7-transmembrane receptor" is

different, the HIV "key" no longer matches the lymphocyte "lock"

and attachment is incomplete. Those cells may avoid infection by

HIV. Tight attachment of the viral particle to receptors on the

lymphocyte membrane enables fusion with the cell membrane.

The viral contents, including viral RNA (shown in yellow) then

empty into the cell's cytoplasm.

Like other viruses that infect human cells, HIV commandeers

the host's machinery to make multiple copies of itself.

2、Reverse Transcription: Converting viral RNA into DNA

An enzyme (protein) that's part of the human

immunodeficiency virus reads the sequence of viral RNA nucleic

acids that have entered the host cell and transcribes the

sequence into a complementary DNA sequence. That enzyme is

called "reverse transcriptase" . Without reverse transcriptase, the

viral genome couldn't become incorporated into the host cell,

and couldn't reproduce.

Reverse transcriptase sometimes makes mistakes reading the

RNA sequence. The result is that not all viruses produced in a

single infected cell are alike.

3、Integration of Viral DNA

Once the viral RNA has been reverse-transcribed into a

strand of DNA, the DNA can then be integrated (inserted) into

the DNA of the lymphocyte. The virus has its own enzyme called

"integrase" that facilitates incorporation of the viral DNA into the

host cells DNA. The integrated DNA is called a provirus.

4、Transcription: Back to RNA As long as the lymphocyte is not activated or "turned-on",

nothing happens to the viral DNA. But if the lymphocyte is

activated, transcription of the viral DNA begins, resulting in the

production of multiple copies of viral RNA. This RNA codes for

the production of the viral proteins and enzymes (translation)

and will also be packaged later as new viruses.

5、Translation: RNA -> Proteins

There are only 9 genes in the HIV RNA. Those genes have the

code necessary to produce structural proteins such as the viral

envelope and core plus enzymes like reverse transcriptase,

integrase, and a crucial enzyme called a protease.

6、Viral Protease

When viral RNA is translated into a polypeptide sequence,

that sequence is assembled in a long chain that includes several

individual proteins (reverse transcriptase, protease, integrase).

Before these enzymes become functional, they must be cut from