Cell Bio Chapter 5 DNA and Chromosomes

Genes

unit of heredity containing the instructions that dictate the characteristics or phenotype of an organism, in molecular terms, segment of DNA that directs the production of a particular protein or FUnctional RNA molecule

Wilkins and Franklin

examined DNA using x ray diffraction to determine its three dimensional atomic structure

Watson and Crick

“discovered” the double helical structure of DNA

Deoxyribonucleic acid (DNA)

double stranded polynucleotide formed from two separate chains of covalently linked deoxyribonucleotides; serves as the cell’s store of genetic information that is transmitted from generation to generation

Adenine, Guanine, Thymine, Cytosine

nucleotide building blocks of DNA (ATCG)

Nucleotides

building blocks of DNA composed of a nitrogen containing base and a 5 carbon sugar that a phosphate group is attached to; covalently link through a phosphodiester bond each other making a sugar phosphate backbone

5’ end

end of DNA that contains the phosphate group

3’ end

end of DNA that contains the hydroxyl group

Double helix

the typical structure of a DNA molecule in which the two complementary polynucleotide strands are wound around each other with base pairing between the strands

Base pair

two complementary nucleotides in an RNA or DNA molecule that are held together by hydrogen bonds (AT CG)

Hydrogen bonds

bonds formed between two DNA strands; two form between A and T while 3 form between G and C

Antiparallel

orientation of DNA bases where they are in opposite positions/polarities of each other; only orientation that DNA base pairs can form hydrogen bonds in

10 pairs

amount of DNA base pairs per helical turn

B form DNA

has 10.5 base pairs per turn

Complementary pairing

when two molecular surfaces fit together and form noncovalent bonds with each other

Chromosomes

long threadlike structure composed of DNA and proteins that carries the genetic information of an organism; becomes visible as a distinct entity when a plant or animal cell prepares to divide

Homologous chromosomes

the maternal and paternal copies of a chromosome

3.1x10^9

the amount of nucleotide pairs of DNA in a full set of human chromosomes aka the human genome

Karyotype

ordered display of the full set of chromosomes of a cell, arranged with respect to size and number

Gene

unit of heredity containing the instructions that dictate the characteristics or phenotype of an organism; in molecular terms, a segment of DNA that directs the production of a particular protein or functional RNA molecule

Genome

the total genetic information carried by all the chromosomes of a cell or organism; in humans the total number of nucleotide pairs in the autosomes is 22 plus the X and Y chromosomes

The smaller the amount of genes

the simpler the organism (not always true)

What is the relationship between gene and chromosome number and genome size?

there is no simple relationship

Cell cycle

the orderly sequence of events by which a cell duplicated its contents and divides into two; consists of G1, S, G2, and M phases

Interphase

stage when chromosomes are duplicated, and expression of genes may occur; DNA replication occurs in this phase

Mitosis

stage when duplicated chromosomes are distributed, or segregated to the two daughter nuclei; gene expression ceases in this phase as well

Interphase chromosomes

long, thin threads of DNA in the nucleus that cannot be easily distinguished in the light microscope

Replication origin

nucleotide sequence at which DNA replication is initiated; multiple of these exist in eukaryotic chromosomes while only one exists in bacterial chromosomes

Telomers

repetitive nucleotide sequence that caps the end od linear chromosomes; counteracts the tendency of the chromosome otherwise to shorten with each round of replication

Centromere

specialize DNA sequence that allows duplicated chromosomes to be separated during M phase; can be seen as the constricted region of a mitotic chromosome

Mitotic chromosomes

more compact highly condensed chromosomes

Chromatid

very long DNA molecules coiled around proteins that has two identical duplicates

Nuclear envelope

pair of concentric membranes that surround the nucleus; something interphase chromosomes attach to at particular sites

Nuclear lamina

protein meshwork that supports the nuclear envelope; another structure interphase chromosomes can attach to

Nucleolus

large structure within the nucleus where ribosomal RNA is transcribed and ribosomal subunits are assembled

Histone

one of a small group of abundant, highly conserved proteins around which DNA wraps to form nucleosomes, structures that represent the most fundamental level of chromatin packing

Chromatin

complex of DNA and proteins that makes up the chromosomes in a eukaryotic cell; long, linear DNA molecule associated with proteins that fold and pact the fine thread of DNA into a more compact molecule

Nucleosome

beadlike structural unit of an eukaryotic cell chromosome composed of a short length of DNA wrapped around an octameric core of histone proteins; includes a nucleosomal core particle (DNA plus histone protein) along with a segment of linker DNA that ties the core particles together

Linker DNA

exposed DNA between core particles

Nucleosome core particle

consists of a complex of eight histone proteins ( 2 HsA, 2 H2B, 2 H3, 2 H4) along with a segment of double stranded DNA 147 nucleotide pairs long that winds around a histone octamer

SMC ring complex

a large ringshaped structure that contains two Structural Maintenance of Chromosomes (SMC) protein subunits at its core; the ring these proteins form is large enough for nucleosomes to pass easily through it. Cohesins and condensins are two major types

Cohesin

a ring shaped SMC protein complex that organizes interphase chromosomes into a long series of large chromatin loops; in addition, a special subset of cohesins holds together the sister chromatids after DNA has been replicated

Sequence specific clamp protein

proteins that stop or stall the moving cohesins and also bind to one drawing DNA together at the base of each loop; its spacing and location determines the size/content of chromosomal loops

Condensins

ring shaped SMC protein complex that compacts duplicated chromosomes for segregation by forming both loops and loops within loops

Chromatin remodeling complex

a family of enzymes (typically multisubunit) that uses the energy of ATP hydrolysis to alter the arrangement of nucleosomes in eukaryotic chromosomes, changing the accessibility of the underlying DNA to other proteins, including those involved in transcription; aka ATP dependent chromatin remodeling complexes

Histone modifying enzymes

enzyme that catalyze the covalent addition of a small molecule, such as a methyl or acetate group, to a specific amino acid side chain on a histone

Heterochromatin

highly condensed region of an interphase chromosome; generally gene poor and transcriptionally inactive

Euchromatin

one of the two main states in which chromatin existing within an interphase cell; prevalent in gene

Epigenetic inheritance

the transmission of gene expression from one cell to its progeny that doesn’t involve altering the nucleotide sequence of the DNA