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The nuclear enveleope makes up the shell of the necleus. It is made up of two unit membranes with a space in between them. It provides a barrier between the genetic information ( DNA ) on the inside and the cytoplasm on the outside. There are pores ( nucleic pores ) that allow material like RNA to enter and exit the necleus.
-Nucleoli ( nucleolus - sing. )
A nucleolus contains parts of various chromosomes to which RNA can get condons from.
Chromatin translated means "colored stuff". It appears as dark and light areas in the nucleus, darker areas closer to the nuclear envelope and lighter areas inbetween the dark areas and deeper to the nuclear envelope.
All of these areas are made of coils of DNA. The dark areas are where very tightly coiled and tightly grouped together strands of DNA exist. The lighter areas are where uncoiled or loosely coiled strands of DNA exist. The dark areas are "condensed chromatin" and the light areas "extended chromatin".
DNA is constructed as a double-helix form, like a spiral staircase. The handrails on the outsides of the staircase are made of glucose ( deoxyribose sugar ) and phosphate groups, alternatingly.
The stairs of DNA are made up of nucleotides bound to each other via hydrogen bonds. Nucleotides generally are made up of one of 5 bases: Adenine ( A ), Cytosine ( C ), Thymine ( T ), Guanine ( G ), and Uracil ( U ).
A, C, and G are common to both DNA and RNA. T goes with DNA and U goes with RNA.
So DNA will be made of dexyribose ( the sugar ), phosphate groups, and bases A, C, G, and T.
RNA is made up of dexyribose ( the sugar ), phosphate groups, and bases A, C, G, and U. RNA is a single strand chain of RNA nucleotides plus dexyribose plus phosphate groups.
Euchromatin - DNA comes in a single strand variety made of its bases, dexyribose, and phosphate groups called euchromatin. In this untwisted, unbound form it is open to be read by mRNA.
DNA unwinds in the extended chromatin, hydrogen bonds between bases are broken. RNA polymerases come along and read the open DNA ( only one side can be read ). RNA polymerases read the DNA in sets of three bases, it reads three bases at a time - each three bases corresponds to one amino acid. RNA polymerase reads and codes the bases as such: read A - write U, rT - wA, rC - wG, rG - wC. The mRNA is now built and encoded and leaves the nucleus via the nuclear pore. The mRNA then finds free ribosome subunits and forms a ribosome.
tRNA is assembled in a similar way, then leaves the nucleus via nuclear pore, goes and collects some amino acids and takes it to the ribosome + mRNA and becomes a functional ribosome and begins assembling proteins.
-Chromatin structure / chromosomes
So, starting from the micro, going to the macro...
DNA starts out as a kind of spiral staircase form ( handrails of deoxyribose and phosphate groups, stairs of pairs of bases bound to each other by hydrogen bonds, forming "nucleotides", the stairs ).
The spiral staircase ( actually double-helix ) begins to coil around itself, collecting histones, disc shaped proteins.
The histones bind together in groups of eight, these groups of eight histones are called nucleosomes. The double-helix then wraps around the nucleosomes.
The nucleosomes stick together forming sort of beads of a necklace with the tightly twisted strand of DNA between them the string, called the "linker DNA".
This necklace then coils around itself even more forming a "tight helical fiber", then coils more to form a "supercoiled structure", then coils more to form a "chromatid" which is sort of an X-shaped structure of two identical DNA strands ( chromosomes ) connected at the centromere.