biologia tema 3

DNA. Chemical composition: deoxyribonucleotides – phosphate, deoxyribose and nitrogenous bases A-T  G-C. Molecular structure: double-stranded structure. Types: Nuclear DNA that forms chromatin, Mitochondrial DNA found in mitochondria and Plastid DNA found in cloroplasts. Cell location: In the nucleus, mitochondria and clororplasts. Function: Contains the organism’s genetic information. RNA. Chemical composition: ribonucleotides – phosphate, ribose, nitrogenous bases A-U  G-C. Molecular structure: single-stranded structure. Types: Messenger RNA (mRNA), Transfer RNA (tRNA), Ribosomal RNA (rRNA). Cell location: In the cytoplasm, free or associated with ribosomes. Function: It synthesises proteins according to the genetic information found in the DNA. DNA replication. When a cell divides, the two resulting daughter cells must have the same genetic information. For this to happen, the DNA forms copies of itself, It replicates irself. This process is called replication (only in DNA). Happens inside the cells’s nucleus and two molecules are obtained form an initial one. This process has to be very precise, if not, the daughter cells would recieve different DNA molecules that have different genetic information. The new molecules are made of two strands. The first is a strand from the original DNA. The second is a complementary new one, meaning it is identical to the original one. This is why this is a semiconservative replication.

Central dogma of molecular biology. Replication: process through which a molecule of DNA duplicates. It takes place in the nucleus. Transcription: process through which a molecule of messenger RNA (mRNA) is synthesised by using a fragment of DNA as a template. (It takes place in the cytoplasm). Translation: process through which a protein is synthesised by using the information contained in the mRNA. (It takes place in the ribosomes). Transcription. is the process through which part of the genetic information is copied from its original form (DNA) into mRNA. Takes places in the nucleus of the cell. mRNA is then released into the cytomplasms through the pores of the nuclear membrane. The mRNA released is complementary to the fragment of DNA that has been transcribed, which is the sequence that codifies a particulas protein that the cell may need. Translation. is the process through which proteins are sybthesised by using the information contained in the mRNA molecules formaede during transcrption (takes places in the ribosomes). Elements need to translation to happen: An mRNA molecules created from the transcription of DNA fragment; Rinosomes; Transfer RNA (tRNA) which RNA molecules that carry amino acids to the tibosomes, a particular type of tRNA transports each type of amino acid; Free amino acids in the cytoplams.

Mutations. DNA is passed on from one generation to the next, in this process, genes do not remain unchaged, sometimes unexpected and random chages occur. These chages are callled MUTATIONS. Only mutations that modify a certain characteristic can be percieved. Mutations can be passed onto offspring. They originate spontaneously (spontagenosu mutations) or result of a mutation. Types: type of the cell affected – somatic, germinal; Cause – spontaneous, induced; Effects – beneficial, neutral, harmful; Resulting alleles – dominant, recessive; Type of genetic alteration – gene, chromosomal, genomic. Mutation acording to the type of genetic alteration: Genetic or molecular mutation – affect chemicall structure of genes; lead to changes in the sequence of amino acids that form protein; as a result, it will alter the way the protein functions.

Chromosomal mutations – affect the structure of chromosomes; they duplicate, elminate or change fragments of themselves; they are percived usinga microscope and occurs in some tumors. Genomic or numeric mutation – affect the number of chromosomes; aneuploidy, lack or excess of chromosomes; euploid, the diploid set of chromosomes is affected into 3n,4n,5n… chromosome insted of 2n. Mutations according to what causes them: Physical mutagens – are radiations that can alter DNA; most important ones are UV rays, gamma rays, X-rays, beta rays. Chemical mutagens – are chemical compouds that alter nucleotides from DNA; most important ones are dyes, some pesticides, pollutants, nicotine, drugs (LSD). Biologicacl mutagens – Viruses; viruses that have genomes with fragments of another cell, these are introduced into the organism they infect, and modify DNA. Transposons; are mobile segments of DNA that change position, altering original DNA.