The cell is the smallest functional unit of human body that can be divided and retain the characteristics necessary for life.
GENETIC Materials:
Genetic information is stored in the structure of deoxyribonucleic acid (DNA). DNA is an extremely stable macromolecule found in the nucleus of each cell. Because of the stable structure of DNA, the genetic information can survive the many processes of reduction division, in which the gametes (i.e., ovum and sperm) are formed, and the fertilization process. This stability is also maintained throughout the many mitotic cell divisions involved in the formation of a new organism from the single-celled fertilized ovum called the zygote. the nucleus of the cell contains the important mechanisms of inheritance. They found that chromatin, the substance that gives the nucleus a granular appearance, is observable in the nuclei of non dividing cells. Just before a cell undergoes division, the chromatin condenses to form microscopically observable, thread like structures called chromosomes.
Genes, the basic unit of inheritance, are contained in chromosomes and consist of DNA. genes are composed of deoxyribonucleic acid (DNA) that provides the genetic blueprint for all proteins in the body. Thus, genes ultimately influence all aspects of body structur and function. Humans are estimated to have 20,000 to 25,000 genes(sequences of DNAthat code for ribonucleic acid [RNA]or proteins)
معاني
establish - يؤلف
stable - مستقر
DNA Structure
The structure that stores the genetic information in the nucleus is a long, double-stranded, helical molecule of DNA. DNA is composed of nucleotides, which consist of phosphoric acid, a five-carbon sugar called deoxyribose, and one of four nitrogenous bases. These nitrogenous bases carry the genetic information and are divided into two groups:
1- The purine bases, adenine and guanine, which have two nitrogen ring structures.
2- The pyrimidine bases, thymine and cytosine, which have one ring. The backbone of DNA consists of alternating groups of sugar and phosphoric acid, the paired bases project inward from the sides of the sugar
______________1
molecule. DNA resembles a spiral staircase, with the paired bases representing the steps.
DNA is an almost universal genetic material, it contains all the instructions necessary to "tell" a living cell what it is supposed to do. there must exist a mechanism that copies DNA faithfully, to ensure that progeny cells contain the same genetic material as the maternal cell
RNA: A second type of nucleic acid, ribonucleic acid is involved in the actual synthesis of cellular enzymes and proteins. Cells contain several types of RNA: messenger RNA, transfer RNA, and ribosomal RNA. Messenger RNA (mRNA) contains the transcribed instructions for protein synthesis obtained from the DNA molecule and carries them into the cytoplasm
انواع الـــ RNA
- -Genes are the fundamental unit of information storage in the cell. They determine the types of proteins and enzymes made by the cell and therefore control inheritance and day-to-day cell function.
- Genes store information in a stable macromolecule called DNA.
- -Genes transmits information contained in the DNA molecule as a triplet code. The arrangement of the nitrogenous bases of the four nucleotides (i.e., adenine, guanine, thymine [or uracil in RNA], and cytosine) forms the code.
- The transfer of stored information into production of cell products is accomplished through a second type of macromolecule called RNA. Messenger RNA transcribes the instructions for product synthesis from the DNA molecule and carries it into the cell's cytoplasm, where ribosomal RNA uses the information to direct product synthesis. Transfer RNA acts as a carrier system for delivering the appropriate amino acids to the ribosomes, where the synthesis of cell products occurs.
- -Although all cells contain the same genes, only a small, select group of genes is active in a given cell type. In all cells, some genetic information is repressed, whereas other information is expressed.
- -Gene mutations represent accidental errors in duplication, rearrangement, or deletion of parts of the genetic code. Fortunately, most mutations are corrected by DNA repair mechanisms in the cell.
_______________2
Besides nuclear DNA, part of the DNA of a cell resides in the mitochondria. Mitochondrial DNA is inherited from the mother by her offspring (i.e., matrilineal inheritance). Several genetic disorders are attributed to defects in mitochondrial DNA
- attributed - يعزى - سنان العزاوي
- contributed - يسهم - الرايب
CHROMOSOMES.
Chromosomes: A single piece of coiled DNA and protein that is found in cell nucleus. Chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the very long DNA molecules to fit into the cell nucleus.
فرق الكروموسوم عن الكروماتين
- الكرومسوم = DNA + protein - ويكون coiled
- الكروماتين = DNA + protein - ويكون granular مع كثافة اعلى
Chromosome forms the classic four arm structure, a pair of sister chromatids attached to each other at the centromere. Centromere is a narrow region that divides the chromosome into short arm and long arm. The short arms are called p arms (from the French petit, small) and the long arms are called g arms (q follows p in the Latin alphabet).
1. Chromatid-one of the two identical parts of the chromosome.
2. Centromere - the point where the two chromatids touch.
3. Short arm.
4. Long arm.
Diagram of a duplicated and condensed metaphase chromosome.
_________________3
Most genetic information of a cell is organized, stored, and retrieved in small intracellular structures called chromosomes. Although the chromosomes are visible only in dividing cells, they retain their integrity between cell divisions. The chromosomes are arranged in pairs; one member of the pair is inherited from the father, the other from the mother.
Each species has a characteristic number of chromosomes. In the human, 46 single or 23 pairs of chromosomes are present. Of the 23 pairs of human chromosomes, there are 22 pairs called autosomes that are alike in males and females. Each of the 22 pairs of autosomes has the same appearance in all individuals, and each has been given a numeric designation for classification purposes.
لماذا يختلف الذكر عن الانثى
- ج\ اختلاف الذكر عن الانثى يكمن في كروموسوم واحد
- حيث في يتشاركون نفس الصفات في 22 كروموسوم ( 22 - autosomes )
- ويختلفون في كروموسوم واحد
The sex chromosomes make up the 23rd pair of chromosomes. Two sex chromosomes determine the sex of a person. All males have an X and Y chromosome (i.e., an X chromosome from the mother and a Y chromosome from the father); all females have two X chromosomes (i.e., one from each parent). Only one X chromosome in the female is active in controlling the expression of genetic traits; however, both X chromosomes are activated during gametogenesis (i.e., formation of the germ cell or ovum).
Important processes:
DNA replication or DNA synthesis is the process of copying double stranded DNA strand, prior to cell division. Replication occurs in the nucleus during the interphase (S) Gives daughter cells a complete set of genetic information identical to the parent cell. The two resulting double strands are identical (if the replication went well), and each of them consists of one original and one newly synthesized strand. This is called semi conservative replication.
Transcription is the process by which an RNA sequence is formed from a DNA template. The type of RNA produced by the transcription process is messenger RNA(mRNA).
الاستنساخ : هي عملية تشكيل ( تخليق ) سلسلة الـ Messenger RNA من قالب الـ DNA , حيث تحدث هذه العملية في نواة الخلية
_______________4
Protein Synthesis
Transcription is followed by TRANSLATION, the synthesis of proteins according to the instructions carried by mRNA. Ribosomal RNA (rRNA) provides the machinery needed for protein synthesis. Transfer RNA (IRNA) reads the instructions and delivers the appropriate amino acids to the ribosome, where they are incorporated into the protein being synthesize.
Cell division
Human body have somatic cells (body cells), which are diploid [2n] having two sets of chromosomes, one from the mother and one from the father. Gametes, reproductive or germ cells, are haploid [one n], they have one set of chromosomes.
انواع الخلايا لدى البشر
- somatic cells - جسدية - diploid ( 2n )
- germ cells - جنسية - haploid ( 1n )
During cell division (mitosis) in non germ cells (somatic cell), the chromosomes replicate so that each cell receives a full diploid number [2n]. In germ cells, a different form of division (meiosis) takes place in which the double sets of 22 autosomes and the 2 sex chromosomes (normal diploid number) are reduced to single sets (haploid number) in each gamete. At the time of conception, the haploid number in the ovum and that in the sperm join and restore the diploid number of chromosomes. So chromosomes are the essential unit for cellular division and must be replicated, divided, and passed successfully to their daughter cells so as to ensure the genetic diversity and survival of daughter cells.
في الوضع الطبيعي يتحول الـ
- ( diploid number - diploid sets) يتحول الى single sets (haploid number) في كل مشيج
- لكن عند الحمل يرجع الـ haploid number الى diploid number
تعليقات
إرسال تعليق