Ch 7

• • Nucleosomes help to supercoil the DNA
• • DNA structure suggested a mechanism for DNA replication
• • DNA polymerases can only add nucleotides to the 3’ end of a primer
• • DNA replication is continuous on the leading strand and discontinuous onthe lagging strand
• • DNA replication is carried out by a complex system of enzymes.
• • Some regions of DNA do not code for proteins but have other important functions
• • Application: Rosalind Franklin’s and Maurice Wilkins’ investigation of DNA structure by X-ray diffraction. (beam of x-rays fired at orderly arranged DNA to get orderly pattern which showed the double helix shape "X")
• • Application: Use of nucleotides containing dideoxyribonucleic acid to stop DNA replication in preparation of samples for base sequencing.
• • Application: Tandem repeats are used in DNA profiling (restriction enzyme could cut on either side of the tandem repeat, see pg 352 tb)
• • Skill: Analysis of results of the Hershey and Chase experiment providing evidence that DNA is the genetic material. - 2x solution of T2 bacteriophage one was 32P(DNA) and other 35S (PROTEIN) -> latch onto E.coli -> only 32P was found in Ecoli showed that DNA was genetic material
• DNA is negatively charged
• helicase unwinds DNA
• DNA primase adds an RNA primer to show DNA polymerase 3 where to go
• single stranded binding proteins prevent seperated DNA strands from reannealing during replication
• • DNA gyrase reduces the torsional strain created by the unwinding of DNA by helicase (via negative super coiling)
• • DNA polymerase 1 removes the RNA primers from the lagging strand and replaces them with DNA nucleotides
• • DNA ligase joins the Okazaki fragments together to form a continuous strand
• • The regions of DNA that do not code for proteins should be limited to regulators of gene expression, introns, telomeres and genes for tRNAs
• • Transcription occurs in a 5’ to 3’ direction
• • Nucleosomes help to regulate transcription in eukaryotes
• • Eukaryotic cells modify mRNA after transcription
• • Splicing of mRNA increases the number of different proteins an organism can produce
• • Gene expression is regulated by proteins that bind to specific base sequences in DNA. eg repressor proteins
• • The environment of a cell and of an organism has an impact on gene expression.
• the promotor region is where RNA polymerase binds, it is near a gene to be transcribed
• direct methylation of DNA tends to inhibit gene expression, the amount of DNA methylation varies during a lifetime and is affected by environmental factors
• RNA polymerase adds the 5 ́ end of the free RNA nucleotide to the 3' end of the growing mRNA molecule.
• • Initiation of translation involves assembly of the components that carry out the process. initiator tRNA carrying start codon -> small subunit -> big subunit
• • Synthesis of the polypeptide involves a repeated cycle of events
• • Disassembly of the components follows termination of translation
• • Free ribosomes synthesize proteins for use primarily within the cell
• • Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes
• • Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane.
• • The SEQUENCE and number of amino acids in the polypeptide is the primary structure.
• • The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding.
• • The tertiary structure is the further folding of the polypeptide stabilized by interactions between R groups.
• • The quaternary structure exists in proteins with more than one polypeptide chain.
• • Application: tRNA-activating enzymes illustrate enzyme–substrate specificity and the role of phosphorylation.
• • Polar and non-polar amino acids are relevant to the bonds formed between R groups
• APE backwards is the tRNA binding sites of the large sub-unit of the ribosome