GENETICS 3: CHROMOSOME STRUCTURE AND FUNCTION

Strausberg (1875)

Chromosomes were first described by this person (include the year) as a thread-like structure which appeared during cell division

Waldeyer (1888)

The term “Chromosome” was first used by ? (Include the year)

Affinity for basic dyes

They were given the term chromosome due to their marked what?

colour, body

Chromosome is derived from the words chroma and soma which means

Chromatin fibers

Chromosomes are composed of thin chromatin threads called?

Folding, Coiling, Supercoiling

Chromatin fibers undergo these processes during prophase so that the chromosomes become progressively thicker and smaller

Light microscope

Chromosomes become readily observable under what?

Fine chromatin threads

At the end of cell division, on the other hand, the fibers uncoil and extend as what? which are not visible at light microscope

Circular or Linear

Chromosomes can be either what?

Single, circular chromosome

Most of Prokaryotic cells have what?

Prokaryotic chromosomes

Numerous examples of prokaryotic cells that have multiple chromosomes, linear chromosomes, or even both. Most of Prokaryotic cells have a single, circular chromosome

Borrelia

This is a notable exception to the arrangement of Prokaryotic chromosome

Borrelia burgdorferi

Bacteria that is the cause of Lyme disease, containing a single linear chromosome and is also under Prokaryotic chromosome

Eukaryotic chromosomes

In contrasts, these cells have multiple linear chromosomes

Circular DNA molecules

This also occur in mitochondria, which are present in almost all eukaryotic cells, and in chloroplasts, which are present in plants and some unicellular eukaryotes

Chromatin

In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called?

DNA and histone proteins

The major components of chromatin are what?

Euchromatin and Heterochromatin

Two types of chromatin can be distinguished:

Euchromatin

This chromatin consists of DNA that is active, e.g. being expressed as protein

Heterochromatin

This chromatin consists of mostly inactive DNA

Mycoplasma genitalium, Eschericha coli k-12, Agrobacterium, tumefaciens, Sinorhhizobium meliloti

Examples of prokaryotic species

1

Number of chromosomes that Mycoplasma genitalium have?

1

Number of chromosomes that Escherichia coli have?

4

Number of chromosomes that Agrobacterium have?

3

Number of chromosomes that Sinorhhizobium meliloti have?

16

Number of chromosomes that the eukaryote Saccharomyces have?

3

Number of chromosomes that the eukaryote Schizosaccharomyces pombe (fission yeast) have?

6

Number of chromosomes that the eukaryote C. elegans(roundworm) have?

5

Number of chromosomes that Arabidopsis thaliana (weed) have?

4

Number of chromosomes that the eukaryote Drosophila melanogaster (fruit fly) have?

Micronucleus 5

Number of chromosomes that the eukaryote Tetrahymena thermophilus have?

Macronucleus 225

Number of chromosomes that the eukaryote protozoa have?

22

Number of chromosomes that the eukaryote Fugu rubripes (fish) have?

19 + x and y

Number of chromosomes that the eukaryote Mus muculus (mouse) have?

22 + x and y

Number of chromosomes that the eukaryote Homo sapiens have?

Single chromosome, Circular

The genomes of prokaryotes are contained in a ______ ___________, which are usually ________ DNA molecules

Histone-like proteins

Prokaryotic chromosome is complexed with wha? that makes it a structured termed the nucleoid

Naked, plasma membrane

Prokaryotic chromosome is sometimes called as a what DNA? and is attached to the?

Plasmids

Prokaryotes also frequently carry one or more smaller independent circular DNAs called?

Bacterial cells

These cells may also contain plasmids

Autonomously self-replicating extrachromosomal DNA

Bacterial cells may also contain plasmids that are?

Bacterial growth, Antibiotic resistance

Unlike larger chromosomal DNA, plasmids typically are not essential _________ ______. Instead, they carry genes that confer desirable traits to the bacteria, such as __________ ___________

Plasmids

Also distinct from chromosomal DNA, they can also be present in many complete copies per cell

Fertility factor (F+ plasmid)

E.g. Antibiotic resistance genes, Plasmids include the what factor?

Relaxed circle, Supercoiled

2 forms of a chromosome

Supercoiled

This is the normal and functional form of a chromosome and is covalently closed circular chromosomes

Relaxed circle

This is an open circular chromosome

One-way prokaryotes, Supercoiling

These types of prokaryotes compress their DNA into smaller spaces through what?

Negatively supercoiled, Positively supercoiled

Genomes can be __________ ___________, meaning that the DNA is twisted in the opposite direction of the double helix, or __________ ___________, meaning that the DNA is twisted in the same direction as the double helix

Normal growth

Most bacterial genomes are negatively supercoiled during?

Positive supercoiling

The helix twists on itself; twists to the right

Negative supercoiling

Most common type of supercoiling, helix twists on itself in the opposite direction; twists to the left

Nucleoid

The circular DNA is packaged into a region of the cell called what?

50 or so loops or domains

The circular DNA is packaged into a region of the cell called the nucleoid where it is organized into how many loops or domains? that are bound to a central protein scaffold, attached to the cell membrane

DNA gyrase

This is necessary for the unwinding of the coils

Topoisomerase

These are enzymes that unwind and wind DNA, in order for DNA to control the synthesis of proteins, and in order for DNA to reproduce. They cut the DNA, and at the end of the process connect it again.

Large linear chromosomes

Eukaryotes possess multiple what?

Chromatin

In eukaryotes, DNA is organized into what?

Chromatin

The complexes between eukaryotic DNA and proteins (histone and non-histone protein) are called what? Which typically contains about twice as much protein as DNA

two chromatids

A chromosome consists of what?

Chromonema

Each chromatid consists of thread like structures that are called?

Chromonemata

Plural word for chromonema

Vejdovsky (1912)

The term chromonema was coined by ? (Include the year)

Chromonemata

This forms the gene bearing portion of chromosomes

Matrix

The mass of achromatic material which surrounds the chromonemata is called?

Pellicle

The matrix is enclosed in a sheath which is known as?

Matrix and Pellicle

Both are non genetic materials and appear only a metaphase, when the nucleolus dissapears

N

the number of different chromosomes in a nucleated cell wall

C

DNA content

23, -3.5 pg

What is the Number of different chromosomes and DNA content a human has

Ploidy

This refers to the number of copies of chromosomes

2n and 2C (somatic cells)

most human cells are diploid what?

Haploid (n and c)

Sperm and egg cells are ?

Small basic proteins (histones)

The DNA of eukaryotic cells is tightly bound to these, that packages the DNA in an orderly way in the cell nucleus

2m

Length of DNA in a human cell is nearly what?

5 to 10um

Diameter of a nucleus

Histones

These are the major proteins of chromatin that are small proteins containing a high proportion of basic amino acids (arginine and hystine) that facilitate binding negatively charged DNA molecules

H1, H2A, H2B, H3, H4

What are the 5 major types of histones

H1

This histone contains a mol. wt. of 22,500 and a number of amino acid 244 and percentage lys + arg 30.8

H2A

This histone contains a mol. wt. of 13,960 and a number of amino acids 129 and percentage lys + arg 20.2

H2B

This histone contains a mol. wt. of 13,774 and a number of amino acids 125 and percentage lys + arg 22.4

H3

This histone contains a mol. wt. of 15,273 and a number of amino acids 135 and percentage lys + arg 22.9

H4

This histone contains a mol. wt. of 11,236 and a number of amino acids 102 and percentage lys + arg 24.5

Histones

DNA double helix is bound to proteins called?

Positively charged amino acids

Histones have what kind of charge?

Non histone chromosomal proteins

Chromatin contains an approximately equal mass of a wide variety of?

Proteins

DNA of prokaryotes is similarly associated with proteins, some of which presumably function as histones do, packing the DNA within the bacterial cell

Histones

These are unique features of eukaryotic cells and are responsible for distinct structural organization of eukaryotic chromatin only

Centromere

The region where two sister chromatids of a chromosome appear to be joined or “held together” during mitotic metaphase is called?

Dark-stained

WHen chromosomes are stained they typically show a __________ region that is the centromere

Primary constriction

Centromere is also termed as

Mitosis

during this phase, the centromere that is shared by the sister chromatids must divide so tat the chromatids can migrate to opposite poles of the cell

Centromere

This is an important component of chromosome structure and segregation

Centromere

First parts of chromosomes to be seen moving towards the opposite poles during anaphase

Satellite DNA

The centromere consists of short repeated DNA sequences that are A-T rich, known as as?

Metacentric, Submetacentric, Acrocentric, Telocentric

Centromeric position and arm length

Metacentric Chromosome

Centromere is located exactly at the center of the chromosome, i.e. both arms are equal in size. Such chromosomes assume V shape at anaphase

Submetacentric Chromosome

Centromere is located on one side of the center point such that one arm is longer than the other. These chromosomes become ‘J’ or ‘L’ shaped

Telocentric Chromosome

Centromere is located at one end of the chromosome so that the chromosome has only one arm. These chromosomes are ‘I’ shaped or rod shaped

two arms,p and q

The centromere divides the chromosome into?