Unit 3

Chromosome

A discrete unit of genetic material composed of DNA and associated proteins. Eukaryotes have this in their cell nuclei and in plastids and mitochondria

Transformation

A type of gene transfer between bacteria in which a segment of DNA from the environment is taken up by a competent cell and incorporated into the bacterial chromosome

DNAase

An enzyme that digests DNA

RNase

An enzyme that digests RNA

Protease

An enzyme that cuts proteins into smaller polypeptides

Nucleic Acid

An organic macromolecule composed of nucleotides. The two types of these are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

Nucleotide

An organic molecule having three components: one or more phosphate groups, a five-carbon sugar (either deoxyribose or ribose), and a single or double ring of carbon and nitrogen atoms known as a base

Strand

A structure of DNA (or RNA) formed by the covalent linkage of nucleotides in a linear manner

Double Helix

Two strands of DNA hydrogen-bonded with each other. In this, two DNA strands are twisted around one another to form a structure that resembles a spiral staircase

Genome

The complete genetic material of an organism or species

Purine

Either of the bases adenine (A) and guanine (G), which have a fused double ring of carbon and nitrogen atoms

Pyrimidine

Any of the bases thymine (T), cytosine (C), and uracil (U), which have a single ring of carbon and nitrogen atoms

Adenine (A)

A purine base found in DNA and RNA

Guanine (G)

A purine base found in RNA and DNA

Thymine (T)

A pyrimidine base found in DNA

Cytosine (C)

A pyrimidine base found in DNA and RNA

Uracil (U)

A pyrimidine base found in RNA

Phosphodiester Linkage

Refers to a double linkage (two phosphoester bonds) that holds together adjacent nucleotides in DNA and RNA strands

Backbone

The liner arrangement of phosphates and sugar molecules in a DNA or RNA strand

Directionality

In a DNA or RNA strand, refers to the orientation of the sugar molecules within that strand, which can be 5’ to 3’ or 3’ to 5’

Base Pair

The structure in which two bases in opposite strands of DNA are held together by hydrogen bonding to each other

AT/GC Rule

Refers to the phenomenon that an adenine (A) in one DNA strand always hydrogen-bonds with a thymine (T) in the opposite strand, and a guanine (G) in one strand always hydrogen-bonds with a cytosine (C) in the opposite strand

Complementary

The characteristic of the two strands of DNA that is due to the specific base pairing that occurs between nucleic acids: A pairs only with T (in DNA) or U (in RNA), and G pairs only with C

Antiparallel

The arrangement in DNA where one strand runs in the 5’ to 3’ direction and the other strand is orientated in the 3’ to 5’ direction

Major Groove

A wider groove that spiral around the DNA double helix. It provides a location where a protein can bind to a particular sequence of bases and affect the expression of a gene

Minor Groove

A groove that spirals around the DNA double helix but is smaller than the major groove

Chromosome

A discrete unit of genetic material composed of DNA and associated proteins. Eukaryotes have these in their cell nuclei and in plastids and mitochondria

Chromatin

The complex of DNA and proteins that makes up eukaryotic chromosomes

Histones

A group of proteins involved in the formation of nucleosomes, which aid in the compaction of eukaryotic DNA

Nucleosome

A structural unit of eukaryotic chromosomes composed of an octamer of histones (eight histone proteins) wrapped with DNA

DNA Replication

The process by which DNA is copied. The original DNA strands are used as templates for the synthesis of new DNA strands

Daughter Strand

The newly made strand in DNA replication

Parental Strand

The original strand in DNA replication

Semiconservative Mechanism

The correct model for DNA replication. Double-stranded DNA is half conserved following replication, resulting in new double-stranded DNA containing one parental strand and one daughter strand

Conservative Mechanism

In this incorrect model for DNA replication, both parental strands of DNA remain together (are conserved) following DNA replication. The two newly made daughter strands are also joined together

Dispersive Mechanism

In this incorrect model for DNA replication, segments of parental DNA and newly made DNA are interspersed in both strands following the replication process

Template Strand

The DNA strand that is used as a template for RNA synthesis or DNA replication

Origin of Replication

A site within a chromosome that serves as a starting point for DNA replication

Replication Fork

The area where two DNA strands have separated and new strands are being synthesized

Bidirectional Replication

The process in which DNA replication proceeds outward from the origin of replication in opposite directions

DNA Helicase

An enzyme that uses ATP to separate DNA strands during DNA replication

DNA Topoisomerase

An enzyme that alleviates DNA supercoiling during DNA replication

Single-Strand Binding Protein

A protein that binds to both of the single strands of parental DNA and prevents them from re-forming a double helix during DNA replication

DNA Polymerase

An enzyme responsible for covalently linking nucleotides together during DNA replication

Deoxynucleoside Triphosphates

Individual nucleotides with three phosphate groups

DNA Primase

An enzyme that synthesizes a primer for DNA replication

Leading Strand

During DNA replication, a DNA strand made in the same direction that the replication fork is moving. This strand is synthesized as one long continuous molecule

Lagging Strand

During DNA replication, a DNA strand made as a series of small Okazaki fragments that are subsequently connected to each other to form a continuous strand

Okazaki Fragments

Short segments of DNA synthesized in the lagging strand during DNA replication

Processivity

The characteristic of DNA polymerase that keeps it from falling off the template strand as it is synthesizing a new daughter strand

DNA Ligase

An enzyme that catalyzes the formation of a covalent bond between nucleotides in adjacent DNA fragments to complete the replication process

Proofreading

The phenomenon in which DNA polymerase identifies a mismatched nucleotide and removes it from the daughter strand during DNA replication

Telomere

A region at the end of a eukaryotic chromosome where a specialized form of DNA replication occurs

Telomerase

An enzyme that catalyzes the replication of the telomere

Cell Cycle

A series of events that lead to cell division. For eukaryotes, it involves a series of phases in which a cell divides by mitosis or meiosis

Cytogenetics

The field of genetics that involves the microscopic examination of chromosomes

Karyotype

A photographic representation of the chromosomes from an actively dividing cell

Sister Chromatids

The two duplicated chromatids that are still joined to each other after eukaryotic DNA replication

Sex Chromosomes

A distinctive pair of chromosomes that are different in males and females of some species and determine the sex of an individual

Autosomes

All of the chromosomes found in the cell nucleus of eukaryotes except for the sex chromosomes

Diploid

Containing two sets of chromosomes (designated as 2n)

Gamete

A haploid cell that is involved with sexual reproduction, such as a sperm or egg cell

Haploid

Containing one set of chromosomes (designated as 1n)

Homolog

A member of a pair of chromosomes in a diploid organism

Homology

A similarity that occurs due to descent from a common ancestor

G1 Phase

The first gap phase of the eukaryotic cell cycle

S Phase

The DNA synthesis phase of the eukaryotic cell cycle

G2 Phase

The second gap phase of the eukaryotic cell cycle

M Phase

The phase of the eukaryotic cell cycle consisting of the sequential events of mitosis and cytokinesis

Interphase

The portion of the eukaryotic cell cycle consisting of the G₁, S, and G₂ phases, during which the chromosomes are decondensed and found in the nucleus

Mitosis

In eukaryotes, the process in which nuclear division results in two nuclei, each of which receives the same complement of chromosomes

Cytokinesis

The division of the cytoplasm to produce two distinct daughter cells

Cyclin

A protein responsible for advancing a cell through the phases of the cell cycle by binding to a cyclin-dependent kinase

Cyclin-Dependent Kinase (CDK)

A protein responsible for advancing a cell through the phases of the cell cycle. Its function is dependent on the binding of a cyclin

Checkpoint

One of three critical regulatory points found in the cell cycle of eukaryotic cells. At these places, a variety of proteins act as sensors to determine if a cell is in the proper condition to divide

Restriction Point

A point in the cell cycle in which a cell has become committed to divide

Mitotic Cell Division

A process whereby a eukaryotic cell divides to produce two new cells that are genetically identical to the original cell

Asexual Reproduction

A reproductive process that occurs when offspring are produced from a single parent, without the fusion of gametes from two parents

Centromere

The region where the two sister chromatids are tightly associated (this is an attachment site for kinetochore proteins)

Kinetochore

A group of proteins that bind to a centromere and are necessary for sorting the chromosomes

Spindle Apparatus

A structure composed of microtubules that organizes chromosomes in eukaryotes during mitosis and meiosis

Centrosome

A single structure often near the nucleus of a eukaryotic cell that forms a nucleating site for the growth of microtubules (also called the microtubule-organizing center)

Pole

A structure of the mitotic spindle defined by each centrosome

Centrioles

A pair of structures within the centrosome of animal cells. Most plant cells and many protists lack this

Prophase

The phase of mitosis during which the chromosomes condense and the nuclear membrane begins to vesiculate (dissociate into small vesicles)

Prometaphase

The phase of mitosis during which the nuclear envelope completely fragments into small vesicles and the mitotic spindle is fully formed

Metaphase Plate

A plane halfway between the poles of the spindle, along which the sister chromatids align during metaphase in mitosis

Metaphase

The phase of mitosis during which the chromosomes are aligned along the metaphase plate

Anaphase

The phase of mitosis during which the sister chromatids separate from each other and move to opposite poles (the poles themselves also move farther apart)

Telophase

The phase of mitosis during which the centrosomes decondense and the nuclear envelope re-forms

Cleavage Furrow

In animal cells, an area that constricts like a drawstring to separate the cells during cytokinesis

Cell Plate

In plant cells, a structure that forms a cell wall between the two daughter cells during cytokinesis

Meiosis

The process by which haploid cells are produced from a cell that was originally diploid

Bivalent

Homologous pairs of sister chromatids that are associated with each other, lying side by side (also called a tetrad)

Synapsis

The process of forming a bivalent

Crossing Over

The exchange of genetic material between homologous chromosomes during meiosis. Allows for increased variation in the genetic information that each parent may pass to the offspring

Meiosis I

The first division of meiosis in which homologous chromosomes are separated into different cells