BSI Lecture 4 DNA Structure Flashcards
Chromosomes
contain long strands of DNA and associated proteins
How many chromosomes do humans have?
46
How many pairs of autosomes (non-sex chromosomes) do humans have?
22
What are the types of sex chromosomes?
X and Y
What is a Karyotype?
It is the display of all chromosomes in a cell
What is an allele?
One of two or more alternative forms of a gene that arise by a mutation and are found in the same place on a chromosome
What constitutes a normal Karyotype?
Humans have 46 chromosomes total. 22 pairs of autosomes (non-sex chromosomes) and a pair of XX or X and Y sex chromosome
When does the chromosomes have to be packaged very tightly in an organized manner?
During mitosis
When preparing for division, DNA is packed into the _________ chromosomes.
Mitotic
How many levels of packaging are there?
4
What level of packaging is it when threadlike mass of genetic material (DNA and histone proteins) form “beads on a string” (11nm structure)?
Level 1
What is a nucleosome?
Basic structural unit of a chromosome. Histones, DNA, Linker Region
How many turns of DNA helix are wound around the octomeric core of histones?
2
What is the role of histones in DNA packaging?
Acts as spools for DNA helix to wrap around its octomeric core.
What is a linker region?
A linker region is the DNA you see between the two histones or “beads”
Octomeric core consists of two copies of each of the 4 core histone protein ____, ____, ____, and ____
H2A, H2B, H3, H4
Histones are contained in the _______ ________
octomeric core
Level 2 packaging, what is the chromatin fiber width?
30nm
What is the purpose of DNA packaging?
Organize and fit all of the DNA into the nucleus.
What is the difference between mitotic chromosome and an interphase chromosome?
Mitotic chromosomes are ready for replication and interphase chromosomes are not.
Can the same gene produce mRNA and tRNA?
No
Do genes encode lipids and carbohydrates?
No, only proteins are encoded. Lipids and carbohydrates are synthesized.
Loops are condensed into chromosomes (700nm). At what level does this occur?
Level 4
What are telomeres?
DNA sequence at the ends of the chromosomes
Telomeres are repeated DNA sequences which allow the ends of chromosomes to be replicated and also to protect the ends from being mistaken by the cell as broken DNA
True
What is a chromatid?
One of the paired and parallel strands of a duplicated chromosome joined by a single centromere.
What is a sister chromatid?
A duplicate copy of a chromatid joined by the centromere.
What is a centromere?
Specialized DNA sequence that allows duplicated chromosomes to be separated during mitosis.
Where do the mitotic spindle binds?
Centromere
________ is the part of the cell cycle when the cell is not dividing.
Interphase
Packaging of interphase: What percent of the chromosome are highly condensed?
10%
What are heterochromatin?
Highly condensed chromosome
Genes that are considered “off” are located in areas of ______________
heterochromatin
Most regions of the interphase chromosome are less condensed, these area is called ____________
Euchromatin
What level of mitotic chromosome does euchromatin resemble?
Level 2
Each strand of DNA is made up of ________
Nucleotides (deoxyribose, phosphate, and base)
DNA strands run in _________ direction.
Opposite
DNA strands are held together by hydrogen bonds between ________
Bases
The backbone of the DNA strand is called the _________
Sugar-phosphate backbone
The two strands of nucleotides forms a ________
Double helix
The basic building blocks of a nucleotide are
Ribose (sugar), phosphate, and a base
Nucleoside consists of
ribose and base (no phosphate)
What are the 2 Purines and are they single or doubled ringed?
Adenine and Guanine, they are double ringed
What are the 3 Pyrimidines and are they single or doubled ringed?
Cytosine, Thymine, and Uracil, they are single ringed.
How are nucleotides linked?
Via phosphodiester bonds to form a strand of DNA
What bond forms between 3’-OH group of one sugar and 5’-phosphate group of another?
Phosphodiester bonds
Define: Gene
A gene is usually defined as a segment of DNA that contains the instructions for making a particular protein (or RNA, if that is the final product).
What type of RNA is the only one translated into protein?
mRNA
What are the “other” types of RNA?
snRNA, miRNA
RNA are single or double stranded molecules?
single
RNA is composed of ______________ acids
ribonucleic
RNA has an OH group at the _____’ position of sugar.
2’
Besides complementary pairing, what are the other functions of Purines and Pyrimidine?
Energy, metabolism, protein synthesis, regulation of enzyme activity and signal transduction
The difference between ribose and deoxyribose is that ribose has an “OH” and deoxyribose has a single “H” at which carbon?
2’
