Unit 2 - Genomes Flashcards
describe chromosome shape in bacterial and eukaryotic cells (2)
- bacterial chromosome is circular
- eukaryotic chromosome is linear
describe a characteristic of bacterial and eukaryotic cells (2)
- bacterial cells are haploid cells
- eukaryotic cells are diploid cells
haploid
- contain a single set of chromosomes (1 copy of DNA)
diploid
- contains a double set of chromosomes (2 copies of DNA)
describe DNA in bacterial and eukaryotic cells (2)
- DNA in both cells is double-stranded
- difference in packing between prokaryotes and eukaryotes is due to the difference in DNA structure and the vast differences in the amount of DNA (eukaryotes have far more in general)
nucleoid-associated proteins
- packing proteins in bacteria
- proteins do not wrap the DNA around themselves
histones
- packaging proteins in eukaryotes
- wrap DNA into a structure called nucleosomes, DNA is wrapped around histones
How do bacteria package their DNA
- combination of supercoiling and proteins to package their circular genome into a nucleoid
How is supercoiling achieved in bacteria? (3)
- (usually) by cutting one stand of the circular DNA, unwinding by a number of turns, and then resealing the DNA
- causes tension in DNA that is relieved by supercoiling, causing the entire genome to wind up into a smaller volume
- important because bacterial cells are generally small in size
supercoiling (3)
- refers to the winding/unwinding of DNA by topoisomerases (an enzyme) in cells to add strain to DNA
- sometimes all DNA packaging is referred to as “supercoiling” of DNA
- more important in bacteria
nucleoid
- in prokaryotes, a cell structure with multiple loops formed from supercoils of DNA
negative supercoils (2)
- supercoils that result from underwinding
- in most organisms, DNA is negatively supercoiled
positive supercoils
- supercoiling resulting from overwinding
How is DNA packed in eukaryotic cells (2)
- cells also have topoisomerase II enzymes and the DNA is usually supercoiled
- DNA is linear and each DNA molecule forms a single chromosome
describe the first level of packaging of DNA in eukaryotes (3)
- referred to as “beads on a string” where the nucleosomes are the beads and the DNA is the string
- also called a 10-nm fiber in reference to its diameter which is about 5x the diameter of the DNA double helix
- these are the areas of the genome that are transcriptionally active
describe the second level of packaging in DNA in eukaryotes (2)
- chromatin is more tightly coiled forming a 30-nm fiber
- as chromosomes in the nucleus condense in preparation for cell division, each chromosome becomes progressively shorter and thicker as it coils onto itself to form a 300-nm coil, a 700-nm coil and finally a 1400-nm condensed chromosome
chromatin (3)
- formed when huge numbers of nucleosomes are formed and collect together along a DNA strand
- DNA-protein complex formed by packaging of DNA with proteins
- found in eukaryotes
chromatids/chromasomes
- coiled up chromatin in a dense form
chromosome condensation
- progressive coiling of the chromatin fiber, an active, energy-consuming process requiring the participation of several types of proteins
chromosome scaffold
- supporting protein structure in a metaphase chromosome
describe the levels of chromosome condensation
- DNA duplex (2 nm)
- nucleosome fiber (10nm)
- chromatin fiber (30nm)
- coiled chromatin fiber (300nm)
- coiled coil (700nm)
- condensed chomatid (1400nm)
compare the sizes of the eukaryotic chromosome and the bacterial nucleoid (2)
- the eukaryotic chromosome is vastly greater than the size of the bacterial nucleoid
- the volume of fully condensed human chromosome is 5 times larger than the volume of the bacterial cell
genome (2)
- refers to all physical DNA within a cell (some exceptions exist), including DNA that does not code for anything
- genetic material transmitted from parent to offspring
state basic definitions to differentiate between the terms genome, genotype, gene and phenotype
- the genome is all the genetic material of a cell/organism
- a genotype is all the genetic makeup of a cell/organism – the sequence of DNA
- a gene is the unit of hereditary information consisting of a DNA sequence
- a phenotype is an observable characteristic/trait
genotype (4)
- genetic makeup of a cell or organism
- set of instructions or DNA sequences
- relates to the DNA sequences that code for protein or have some other type of function, but it can relate to any sequence of DNA that is important to us
- the particular combination of alleles present in a an individual
phenotype (4)
- expression of a physical, behavioural, or biochemical trait
- an observable phenotype include height, weight, eye colour, etc
- based on the genotype and the environment
- what happens when the instructions are interpreted inside any given cell
homozygous
- describes an individual who inherits an allele of the same type from each parent, or a genotype in which both alleles for a given gene are of the same type
heterozygous
- describes an individual who inherits different types of alleles from the parent, or genotypes where the 2 alleles for a given gene are different
in essence, what is the relationship between the genotype and the phenotype?
- genotype is the DNA’s information and the phenotype is the result of the information being used
alleles
- different forms of a gene, corresponding to different DNA sequences in each different form
How can the regulation of the expression (gene regulation) of protein-coding genes affect the gene products?
- different gene products are made in different amounts in different cells at different times
What is the result of differential gene expression? (2)
- allows some protein-coding genes to be deployed in different combinations to yield a variety of distinct cell types
- proteins can interact with one another so that, even though there are relatively few types of protein, they are capable of combining in many different ways to perform different function
How can a single gene yield multiple proteins?(2)
- alternative splicing (different exons are spliced together to make different proteins_
- post-translational modification (proteins undergo biochemical changes after they have been translated)
gene (2)
- unit of heredity information consisting of a DNA sequence
- DNA sequence within a genome that can code for a protein or RNA
what can contribute to major evolutionary changes?
- acquisition of whole new genes and the modification of existing genes and their regulation in subtle ways
gene regulation
- the various ways in which cells control gene expression
are all genes expressed in all cells and what does it mean? (4)
- no
- this means that the phenotype may not be what you expect based on the presence of a gene in the genotype
- cells in our body all share the same DNA but have vastly difference phenotypes as different sets of genes in the genotype are expressed in different cells
Is there a correlation between the size of a genome and the complexity?
- NO, at least among eukaryotes
Is the number of genes a good predictor of organism complexity?
-NO!
If Species X has 100 million base pairs and Species Y has 96 million base pairs then:
- the genome of species X is larger than the genome of species Y
how are genomes measured?
- measured in number of base pairs
- units are a kilobase (kb), a megabase (one million base pairs Mb), and a gigabase (a billion base pairs Gb)
C-value paradox
- disconnect between genome size and organismal complexity
C-value
- the amount of DNA in a reproductive cell
polyploidy (3)
- condition of having more than 2 complete sets of chromosome in the genome
- especially prominent in many groups of plants
- occurs because of duplication or hybridization
What is the principal reason for large genomes among some eukaryotes?
- genomes contain large amounts of DNA that do not code for for proteins, such as introns and DNA sequences that are present in many copies
