1.1 DNA is stored differently in different organisms.
1.1.1 Nuclear Eukaryotic DNA is Linear and
Associated with Proteins
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.
1.1.2 DNA Molecules are Shorter and Circular in Prokaryotes.
1.2 DNA contains genes.
1.2.1 Gene- A sequence of DNA bases.
1.2.2 Each Amino Acid is coded for by a
sequence of three bases in a gene
called a triplet..
184.108.40.206 The complete set of genes in the cell.
220.127.116.11 Full range of proteins a cell is able to produce.
1.2.5 Functional RNA
18.104.22.168 Genes that don't code for a polypeptide code.
1.3 Most DNA in Eukaryotic cells
Doesn't Code for Polypeptides
22.214.171.124 Section of DNA that don't code for Amino Acids.
126.96.36.199 Removed during Protein Synthesis.
188.8.131.52.1 So thy don't affect the amino acid order.
184.108.40.206 Not present in Prokaryotic DNA.
220.127.116.11 Sections of DNA that do code for DNA.
1.4 Genes can Exist in Different forms called Alleles.
1.4.1 Different Versions of the same Gene.
1.4.2 Order of bases in each allele is slightly different.
18.104.22.168 So code for different versions of the same polypeptide.
1.4.3 Homologus Pairs
22.214.171.124 Alleles coding for the same characteristic will
be found at the same fixed position on each
chromosome in a homologus pair.
2 RNA and Protein Synthesis
2.1 Two types of RNA
126.96.36.199 Messenger RNA
188.8.131.52 Made during transcription.
184.108.40.206 Carries the genetic code
from the DNA to the
ribosomes where t is used
to make a protein during
220.127.116.11 mRNA is a single polynucleotide strand.
18.104.22.168 Three adjacent bases are usually called codons .
22.214.171.124 Transfer RNA
126.96.36.199 Involved in translation. Carries amino acids that are
used to make proteins to the ribosomes.
188.8.131.52 Single polynucleotide strand that's folded into a clover shape.
Hydrogen bonds between specific base pairs hold the molecule
in this shape.
184.108.40.206 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.
2.2 First stage of Protein Synthesis.
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.
220.127.116.11.1 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
18.104.22.168 In prokaryotes mRNA is produced directly from the DNA - without splicing taking place.
2.3 Second stage of Protein Synthesis
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.
2.3.2 Forms a polypeptide chain
3 The Genetic Code and Nucleic Acids.
3.1 Characteristics of the genetic code.
3.1.1 Sequence of Base Triplets
3.1.2 Non - Overlapping
22.214.171.124 Base triplets don't share their bases
126.96.36.199 More possible combinations of triplets than there
re AA. So some AA are coded foor by more than
one base triplet.
3.1.4 Start and Stop codons
188.8.131.52 Same specific base triplets code for
the same AA in all living things.