DNA, RNA and Protein Synthesis.

Nota:

• 1)Eukaryotic cells contain linear DNA molecules that exist as chromosomes thread. 2) DNA molecule is wound up so it can fit into the nucleus. 3) DNA molecule is wound around proteins called histones. 4)Histone proteins also help support the DNA. 5) DNA (and protein) is then coiled up very tightly to make compact chromosomes.  6) The mitochondria and chloroplasts in eukaryotic cells also have their own DNA. This is pretty similar to prokaryotic DNA. It isn't associated with proteins.

1. Supercoiling

1. The complete set of genes in the cell.

1. Full range of proteins a cell is able to produce.

1. Genes that don't code for a polypeptide code.
2. tRNA
3. rRNA

1. Section of DNA that don't code for Amino Acids.
2. Removed during Protein Synthesis.
   1. So thy don't affect the amino acid order.
3. Not present in Prokaryotic DNA.

1. Sections of DNA that do code for DNA.

1. So code for different versions of the same polypeptide.

1. Alleles coding for the same characteristic will be found at the same fixed position on each chromosome in a homologus pair.
   1. Locus.

1. Messenger RNA
2. Made during transcription.
3. Carries the genetic code from the DNA to the ribosomes where t is used to make a protein during translation.
4. mRNA is a single polynucleotide strand.
5. Three adjacent bases are usually called codons .

1. Transfer RNA
2. Involved in translation. Carries amino acids that are used to make proteins to the ribosomes.
3. Single polynucleotide strand that's folded into a clover shape. Hydrogen bonds between specific base pairs hold the molecule in this shape.
4. Every tRNA molecule has a specific sequence of three bases at one end called an anticodon. They also have an amino acid binding site at the other end.

Nota:

• 1) Transcription starts when RNA polymerase attaches to the DNA double- helix at the beginning of a gene. 2) H-bonds break, separating the strands, and the DNA mol. uncoils at the point exposing some of the bases. 3) One of the strands is then used as a template to make an mRNA copy. 4) RNA polymerase lines up free RNA  nucleotides alongside the exposed bases on the template strand. Speecific, complimentary base pairing means that the mRNA strand ends up being a complimentary copy of the DNA template strand. 5) Once the RNA nucleotides have paired up with their specific bases on the DNA strand, they're joined together by RNA polymerase, forming a mRNA molecule. 6) The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand. 7) The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double helix. 8) When RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making mRNA and detaches from the DNA. 9) In eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where the next stage of protein synthesis takes place.

1. Eukaryotes
   1. Introns and exons are both copied into mRNA during transcription. mRNA strands containing introns and exons are called pre-mRNA . a process called splicing then occurs- introns are removed and the exons joined tgether-forming mRNA strands this takes place in the nuleus. The mRNA leaves for translation
2. In prokaryotes mRNA is produced directly from the DNA - without splicing taking place.

Nota:

• 1) the mRNA attaches itself to a ribosome and transfer RNA  molecules carry amino acids to it. energy requred from ATP. 2) A tRNA mol. (carrying an amino acid), with an anti-codon that's complimentary to the first codon on the mRNA , attaches itself to the mRNA by specific base pairing. 3) a second tRNA molecue attaches itself to the next codon on the mRNA in the same way. 4) The two AA attached to the tRNA molecules are joined by a peptide bond. The first tRNA mol. moves away, leaving the AA behind. 5) A third tRNA mol. binds to the nexxt codon on the mRNA. It's AA binds to the first two and the second tRNA mol. moves away. 6) This process continues, producing a chain of linked AA until there's a signal on the mRNA molecule. 7) The polypeptide chain moves away from the ribosome and translation is complete.

1. Codon

1. Base triplets don't share their bases

1. More possible combinations of triplets than there re AA. So some AA are coded foor by more than one base triplet.

1. Same specific base triplets code for the same AA in all living things.