Module 2 - The Molecular Basis of Inheritance Flashcards
Genetic material must perform three essential functions. What are they?
Replication - the genotypic function. Each cell must be replicated from a single cell into daughter cells.
Gene expression - the phenotypic function. Genes control colour and shape.
Mutation - the evolutionary function. Through mutations different phenotypes (colours) are achieved.
Purines are _____ _____ structures, and are nucleotides ___ and ___. Pyrimidines are _____ _____ structures and are nucleotides ___ and ___. A and T have _____ hydrogen bonds while C and G have _____. New nucleotides must connect to the ____ ____ ____.
Double ring, A, G, single ring, T, C, two, three, free 3’OH group.
What is Chargaff’s rule?
States that DNA from any cell of all organisms should have a 1:1 ration (base pair rule) of pyrimidine and purine bases, and that the amount of guanine should equal cytosine and and the amount of adenine should equal thymine.
There is a two step process by which the information in genes flows into proteins. Describe this model.
The Central Dogma
DNA -> RNA -> Protein
^ ^ ^
| ^ ^ replic.
Name three forces that stabilise the DNA double helix.
Covalent bonds - sugar phosphate backbone
Hydrogen bonds - between bases
Hydrophobic interactions - bases
In the structure of DNA, DNA is negatively charged and histones are positively charged. The Solenoid & Zigzag models describes the condensation of DNA. How is the DNA mitotic chromosome formed from simple DNA molecules? How do positivity and negativity influence this process?
The DNA molecules (single histone proteins) start off at 2nm in length. These condense into nucleosomes, which consist of eight histone proteins wound together with linker DNA (think beads-on-a-string structure) - these make up the 11nm fibre. In vivo, these nucleosomes interact with each other to coil more tightly and produce the 30nm chromatin fibres. Finally, these chromatin fibres are densely coiled together to produce the 300nm mitotic metaphase chromosome.
As the positivity of the surrounding chemical environment increases, the condesation also increases. As the positivity decreases, condensation decreases.
What causes ageing in terms of molecular DNA? Describe the structure and function of these.
Ageing is caused by the shortening of telomeres over time (the ends of a eukaryotic chromosome). Telomeres of cancer cells and germ-line cells do not deteriorate.
Telomeres form structures called t-loops which function to protect the free end of a DNA molecule from deoxyribonucleases and fusion with other chromosomes. They also facilitate the complete replecation of the ends of linear DNA molecules.
DNA replication is semi-conservative - name the three stages of DNA replication in order.
Initiation, elongation, termination.
Describe bacterial replication.
- dsDNA bidirectionally unwinds at the oricyte, producing ssDNA templates for synthesis of new DNA.
- A replication bubble forms, usually having a replication for at each end.
- The forks proceed around the circle.
- Eventually two circular DNA molecules are produced.
Describe the requirements and functions of DNA polymerase I.
DNA polymerase I requires a primer with a free 3’OH, template DNA, substrates and Mg2+.
It synthesises the phosphorus trinucleotide at the terminus of the primer strand. It contains exonuclease activity that cuts (corrects) DNA strands. It is also able to proofread strands (mostly removes primers).
Describe continuous and discontinuous DNA synthesis.
The synthesis of the leading strand is continuous as it must progress in a 5’ - 3’ direction. The synthesis of the lagging strand is discontinuous and is synthesised in short segments called Okazaki fragments.
The Replication Apparatus
Formation of replication fork. Synthesis of new DNA strands initiated by ____ ____ and synthesised by _____ _____.
The discontinuous replication of the ______ strand requires an _____ _____ to start the synthesis of each _____ _____.
DNA _____ unwinds the double helix and DNA _____ synthesises the RNA ______ for successive Okazaki fragments. RNA primers are covalently ______ with ______ by DNA _____ ___. RNA primers are replaced with DNA by _____ _____ ___. Single stranded _____ left by polymerase are sealed with _____ ____.
RNA primers, DNA primase. Lagging, RNA primer, Okazaki fragment. Helicase, primase, primers. Extended, deoxyribonucleotides, polymerase III. DNA polymerase I. Breaks, DNA ligase.
What is the function of telomerase?
To extend telomere length on the lagging strand’s 3’ end, so the whole DNA sequence can be synthesised.
What are the three functional units of a gene?
Promoter - DNA sequence. “Upstream” of coding sequence. Acts as “on/off” or “dimmer” switch (high/low).
Coding sequences - sequence when transcribed into RNA contains information to synthesise proteins.
Termination sequence - end point.
What are the three additional features of eukaryotic transcription?
- 7 methyl guanosine cap added to the 5’ of primary transcript
- poly(A) tail added to the 3’ of the primary transcript
- removal of intron sequences
