exam 3 biology

Adenine (A)-

A nitrogenous base found in DNA. It is a purine and pairs with thymine (T) through two hydrogen bonds. It is one of the four bases that make up DNA.

Cytosine (C)-

A nitrogenous base found in DNA. It is a pyrimidine and pairs with guanine (G) through three hydrogen bonds

Guanine (G)-

A nitrogenous base found in DNA. It is a purine and pairs with cytosine (C) through three hydrogen bonds.

Thymine(T)-

A nitrogenous base found in DNA. It is a pyrimidine and pairs with adenine (A) through two hydrogen bonds.

Base pair-

Two complementary nitrogenous bases that bond together in DNA. Adenine pairs with thymine (A–T), and guanine pairs with cytosine (G–C).

Complement-

A DNA strand that has bases matching the complementary base-pairing rules of another strand. A pairs with T, and G pairs with C.

Purine-

A type of nitrogenous base with a double-ring structure. Adenine and guanine are purines.

Pyrimidine-

A type of nitrogenous base with a single-ring structure. Cytosine and thymine are pyrimidines.

Nucleotide-

The building block of DNA. Each nucleotide contains a phosphate group, a five-carbon sugar (deoxyribose), and a nitrogenous base.

DNA polarity-

The direction of a DNA strand, which has a 5′ end and a 3′ end. DNA strands run in opposite directions (antiparallel), and new DNA is built in the 5′ to 3′ direction.

Chromatin-

DNA wrapped around proteins called histones. It is the material that makes up chromosomes and is usually less condensed when the cell is not dividing.

Histone-

A protein that DNA wraps around to help organize and package DNA inside the nucleus.

Nucleosome-

A section of DNA wrapped around a group of histone proteins. It is the basic unit of DNA packaging.

Chromosome-

A structure made of DNA and proteins that contains genetic information (genes). Chromosomes become more condensed and visible during cell division.

Gene-

A segment of DNA that contains instructions for making a functional product, such as a protein or RNA.

Genome-

The complete set of genetic information (DNA) contained in an organism.

Allele-

An alternative version of a gene. Different alleles can produce variations in inherited traits.

Homologous chromosome pairs

Pairs of chromosomes that have the same genes in the same locations, with one chromosome inherited from each parent. They may carry different versions (alleles) of the same genes.

Sister chromatids-

Two identical copies of a chromosome that are attached together at the centromere after DNA replication.

Centromere-

The region of a chromosome where sister chromatids are attached. It is also where the kinetochore forms.

Kinetochore

-A protein structure that forms at the centromere and allows spindle fibers to attach to chromosomes during cell division.

Centriole-

A cylindrical structure made of microtubules that helps organize the spindle during animal cell division.

Centrosome-

The main microtubule-organizing center in animal cells. It helps organize spindle fibers during cell division and contains a pair of centrioles.

Spindle-

A structure made of microtubules that attaches to chromosomes and helps move them during cell division.

Telomeres-

Protective sections of repetitive DNA found at the ends of chromosomes. They help prevent chromosomes from losing important genetic information.

DNA replication-

The process of making an identical copy of DNA before cell division so that each new cell receives a complete set of genetic information.

Semi-conservative-

Describes how DNA replicates. Each new DNA molecule contains one original strand and one newly made strand.

Replication origin-

The specific location on a DNA molecule where DNA replication begins.

DNA helicase-

An enzyme that unwinds and separates the two DNA strands by breaking the hydrogen bonds between complementary bases.

Single-stranded binding proteins-

Proteins that attach to separated DNA strands and keep them from reconnecting during DNA replication.

DNA topoisomerase-

An enzyme that relieves twisting and tension ahead of the replication fork as DNA is unwound.

DNA polymerase-

An enzyme that builds new DNA strands by adding complementary nucleotides in the 5′ to 3′ direction. It also helps proofread newly made DNA.

DNA ligase-

An enzyme that joins pieces of DNA together by sealing gaps in the sugar-phosphate backbone, especially between Okazaki fragments.

RNA primer-

A short piece of RNA that provides a starting point for DNA polymerase to begin adding DNA nucleotides.

Leading strand-

The new DNA strand that is made continuously in the 5′ to 3′ direction toward the replication fork.

Lagging strand-

The new DNA strand that is made discontinuously in short sections (Okazaki fragments) away from the replication fork.

Okazaki fragments-

Short sections of newly made DNA that form on the lagging strand during DNA replication. DNA ligase joins them together.

Proofreading-

The process in which DNA polymerase checks newly added nucleotides for mistakes and corrects errors during DNA replication.

Initiation-

The first stage of DNA replication, when replication begins at the origin and the DNA strands are separated.

Elongation-

The stage of DNA replication when DNA polymerase adds complementary nucleotides to build the new DNA strands.

Termination-

The final stage of DNA replication, when the copying of DNA is completed.

Interphase-

The stage of the cell cycle when a cell grows, performs its normal functions, and prepares for division. It includes G1, S, and G2 phases.

Gap 1 (G1)-

The first stage of interphase. The cell grows, performs normal functions, and makes proteins and organelles needed for later stages.

S Phase-

The stage of interphase when DNA replication occurs. Each chromosome is copied, producing two identical sister chromatids.

Gap 2 (G2)-

The final stage of interphase. The cell continues growing, checks the replicated DNA, and prepares for cell division.

Prophase-

The first stage of mitosis. Chromatin condenses into visible chromosomes, the spindle begins forming, and the nucleolus disappears.

Prometaphase-

The stage of mitosis when the nuclear envelope breaks down and spindle fibers attach to chromosomes at their kinetochores.

Anaphase-

The stage of mitosis when sister chromatids separate and are pulled toward opposite ends of the cell.

Telophase-

The final stage of mitosis. Chromosomes reach opposite ends of the cell, begin to uncoil, and new nuclear envelopes form around them.

Cytokinesis-

The process of dividing the cytoplasm to produce two separate daughter cells after nuclear division.

Cleavage furrow-

The indentation that forms in an animal cell during cytokinesis as the cell membrane pinches inward to separate the two daughter cells.

Bivalent-

A pair of homologous chromosomes that come together during prophase I of meiosis. Each chromosome contains two sister chromatids.

Tetrad-

A group of four chromatids formed when two homologous chromosomes pair together during meiosis I.

Chiasmata

-The visible points where homologous chromosomes are connected after crossing over occurs during meiosis.

Crossing over-

The exchange of DNA segments between nonsister chromatids of homologous chromosomes during prophase I of meiosis. It creates genetic variation.

Diploid (2n)-

A cell that contains two complete sets of chromosomes, one set inherited from each parent. Most human body cells are diploid and contain 46 chromosomes.

Haploid (n)-

A cell that contains only one complete set of chromosomes. Human sperm and egg cells are haploid and contain 23 chromosomes.

Somatic-

Refers to body cells that are not reproductive sex cells (gametes). Human somatic cells are normally diploid.

Template strand-

The original DNA strand that serves as a guide for building a new complementary DNA strand during replication.