Chapter 5 Concepts Flashcards
What is the organisms genome?
The total genetic information carried by a cell or an organism (or the DNA molecules that carry this information).
What is Chargaff’s Rule?
[A]=[T], [C]=[G]
What type of bonds are formed between A-T and C-G basepairs?
hydrogen bonds (2 for A-T and 3 for G-C basepairs)
Does the double stranded DNA have polarity? What does that mean?
Yes. Strands run in opposite directions
Is the chromosome one long double stranded DNA molecule?
Yes
What is on the 3’ end of the DNA?
Hydroxyl
What is on the 5’ end?
phosphate
What is a nucleosome?
DNA wrapped around protein core of 8 histone molecules (bonded ionically)
How many times does DNA wrap around the nucleosome?
1.7 turns left handed
How many histones comprise the nucleosome core?
8 histone proteins: 2-H2A, 2-H2B, 2-H3, 2-H4
What part of the histone sticks out of the nucleosome and can be modified by acetylation, phosphorylation, methylation?
N terminal tail
How would you define a gene?
A discrete segment of the genome composed of introns and exons that codes for a polypeptide or an RNA molecule and contains a promoter region and a terminator region
Where are genes located?
Genes are located on the chromosomes
How is gene structure in a prokaryote?
genes are often organized as functional units called operons, do not have introns, have specific promoter sequences and terminator sequences, a single mRNA in bacteria can encode multiple discrete polypeptides
How is gene structure in a eukaryote?
genes located throughout 23 chromosomes in humans, made of introns and exons, and dispersed throughout the genome, have promoter region and terminator region and normally only encode a single polypeptide (but alternative splicing can result in addition of unique exons in a gene leading to splice variants that have additional polypeptides that are added to the protein–these are often in the form of domains)
Do bacteria have introns and exons?
No
What are exons?
parts of DNA sequence of a gene that will make up the mature mRNA.
What are introns?
Segments of DNA between exons that are not included in the mature mRNA
Approximately how many genes are in the human genome?
24,000
What are the structures that cap the end of linear chromosomes?
7-methylguanosine CAP (unusual triphosphate linkage and methylation of the 2’ position)
What is the enzyme that adds the ends to linear chromosomes?
Telomerase
What is telomerase composed of?
It is an enzyme that is composed of both RNA and protein (carries its own primer as an RNA to anneal and extend the telomere repetitive ends)
What is chromatin?
The complex of several classes of protein with nuclear DNA (proteins that bind to the DNA to form eucaryotic chromosomes, including histones, and other DNA binding proteins such as transcription factors)
What are three main components of eucaryotic chromosomes that are associated with heterochromatin?
Centromere, Telomeres, Origins of Replication
What is heterochromatin?
most highly condensed interphase chromatin
What is euchromatin?
other form of interphase chromatin; less condensed form
What are chromatin loops?
Loops are open areas of chromatin (not in heterochromatin) that contain genes that are actively expressed
If an area of chromatin has high levels of methylation of cytosines, will it express genes in that region or not?
Gene will most often be silenced
Where are ribosomes formed?
in the nucleolus that is located in the nucleus (ribosomes are made of RNA and proteins; ribosomal RNA is transcribed by RNA polymerase I)
If an active gene area is moved next to a region of heterochromatin by translocation, what will happen to the expression of those genes?
silence the gene (heterochromatin is very tightly condensed)
Where is heterochromatin located in the nucleus generally?
near the periphery
Are there certain types of histones that are associated with specific types of heterochromatin?
yep (ex: HP-1 associated with heterochromatin, and there are specific histones for the centromere and origins of replication)
How do histones interact with DNA and what types of amino acids are they enriched in?
DNA wraps around histone core 1.7 times left handed. “Enriched” or strengthened by positively charged amino acids (lysine, arginine) because they pull the chromatin in even tighter
What does histone H1 do?
Pair of long tails at N and C terminal (C terminal attaches to chromatin pulling it in closer)
How do chromatin remodelling complexes work?
use energy of ATP hydrolysis to change the position of the DNA wrapped around nucleosomes, decondensing underlying DNA (increases transcription)
During mitosis, what level of compaction of the chromatin is achieved?
A lot. 10,000-fold
What is the 30nm fiber?
In the 30nm fiber nucleosomes are arranged in groups of 6; a group of 6 nucleosomes has 1200bp of DNA
What would be a way that cells could pass on to daughter cells a certain level of compaction of some chromatin and openness of other chromatin areas?
Reads methylation indicators (markers) and places methyl groups on the same C-G pair on the new daughter strand; methylation causes compaction (could silence gene)
