BIO372H5 Lecture Notes - Lecture 4: Okazaki Fragments, Helicase, Dna Replication

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hassan_rizvi96

17 Jan 2020

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7-binding and unwinding: origin selection and activation by the initiator protein. Eukaryotic chromosomes are replicated exactly once per cell cycle. Dna replication occurs only in s phase (during mitosis). Addition of one or two more copies of critical regulatory genes. Around 1000 replicator sequences in a single chromosome. Multiple of replicators (e. g. origin 3 and 5) must be activated to ensure that each chromosome is fully replicated during each s phase. Replicator 2 and 4 is passively replication. Replicated without initiation as there is already initiation around these replicators. Activation of the parental replicator results in the inactivation of the replicator on the daughter dna. Origin 3 and 5 initiatie origin 1 initiates; origin 2 is passively replication. Required to separate daughter dna molecules during replication. After replication of a circular dna chromosome is complete, the two circular dna molecules must be disengaged from each other.

Related Questions

The bacterium E. coli, which is a major model system for the study of genes and DNA, has a singular circular chromosome of about 4x106 bp. In contrast, human diploid cells have __1__ chromosomes, of __2__ different types (donât forget that the X Â¹ Y!). The total amount of DNA found in a haploid cell such as a sperm or egg is called the organismâs âC-valueâ; the human C-value is __3__.

Also in contrast to the E. coli circular chromosome is the fact that eukaryotic chromosomes are not circular, but instead are __4__. Eukaryotic chromosomes are complexed heavily with protein to form a DNA-protein complex generically called __5__. The proteins found can be considered to fall into two general classes: __6__ and __7__. The first class is made up of 5 major proteins called __8__, __9__, __10__, __11__, and __12__. On a weight to weight basis, these proteins make up about __13__% of the total mass of a chromosome. Since these proteins must associate relatively non-specifically with DNA, they are rich in the basic amino acids __13__ and __14__, which gives the proteins a net __15__ charge.

One goal of packaging the DNA into chromatin is to compact the genome so it will fit into a nucleus. The basic unit of chromatin structure is the __16__, which has __17__ base pairs of DNA wrapped around a âcore particleâ composed of __18__ copies each of the core histones. Each nucleosome is separated by a stretch of âlinkerâ DNA so that the repeating unit is approximately 200 bp. Lets do a little arithmetic: If we consider that the nucleosome is approximately __19__ nm in diameter, that there is about 200 bp in this structure, and that 200 bp of DNA would normally occupy __20__ nm if stretched out straight (recall that each base is spaced about 0.34 nm from the next), we can see that the nucleosome alone allows for a __21__-fold compaction ratio.

The nucleosome structure is further compacted by histone __22__, which is not a part of the core particle. Instead, this histone __23__ (does what?) to cause the nucleosomal 10 nm fiber to condense into a higher-order structure referred to as the __24__ nm fiber. In the nucleus, chromosomes do not just float around freely: they are tethered to a proteinaceous structure called the __25__ at specific DNA regions called âSARsâ, which stands for __26__. SARs are rich in topoisomerases, to allow the winding and unwinding of the DNA that accompanies replication and transcription to occur, despite this constraint.

The 30 nm fiber discussed above is the form in which transcriptionally active DNA is believed to exist in the nucleus; however, further condensation leads to a highly condensed inactive form called __27__; in this terminology, the active form is referred to as __28__. The inactive condensed form can be divided into two types: one type is essentially invariant between cell types, and since it is âon all t timeâ, it is referred to as __29__. The other type comes and goes, depending on the expression of the genes present in that region of the chromosome; it is referred to as __30__.

Eukaryotic chromosomes carry the genes, of course, but also have other functional regions. One such region is the place where the spindle apparatus attaches during mitosis and meiosis; this region of the chromosome is called the __31__. Another important part of the linear eukaryotic chromosome is the ends; these are called __32__. In humans, the end of each chromosome is composed of many repeats of the short sequence __33__. One more type of functional region on each chromosome is the place where DNA replication starts; in humans, each chromosome has several of these __34__. Thus, eukaryotic chromosomes carry several different types of functional sequences, which together allow for their __35__ during S phase, __36__ during mitosis and meiosis, and the __37__ of their genes

20. All living things must maintain a constantinternal environment to function properly through the process of__. (Points : 2)

metamorphosis
alkalosis
homeostasis
cryogenesis

Question 21.21. Glucose, fructose, sucrose,starch and glycogen are all examples of ___. (Points : 2)

proteins
carbohydrates
lipids
nucleic acids

Question 22.22. Some insects can "walk onwater" because __. (Points : 2)

water has a high surfacetension
water is adhesive
water istransparent
water expands when itfreezes

Question 23.23. To overcome an energy barrierbetween reactants and products in a chemical reaction, energy mustbe provided to get the reaction started. This energy is called ___energy. (Points : 2)

potential
reaction
initiation
activation

Question 24.24. Where in the cell doesglycolysis takes place? (Points : 2)

lysosomes
cytoplasm
mitochondria
nucleus

Question 25.25. Photosynthesis uses sunlightto convert water and carbon dioxide into __. (Points : 2)

carbon dioxide andwater
oxygen and sugars
proteins and sugars
carbon dioxide andoxygen