QCAA Biology: Unit 4

Gene

Region/s of DNA that are made up of

nucleotides; the molecular unit of heredity.

Genome

All the genetic material in the

chromosomes of an organism, including its

genes and DNA sequences.

DNA (Deoxyribonucleic Acid)

A complex nucleic acid which contains the genetic information that makes up the chromosomes.

RNA (Ribonucleic Acid)

Single-stranded nucleic acid that contains the sugar ribose.

Nitrogenous Bases

Adenine, Guanine, Cytosine, Thymine, Uracail.

Phosphate Group

A functional group consisting of a phosphorus atom covalently bonded to four oxygen atoms.

Nucleotides

Basic units of DNA molecule, composed of a sugar, a phosphate, and one of 4 DNA bases.

Pentose Sugar

A five-carbon sugar (deoxyribose or ribose) molecule found in nucleic acids.

Purines

Bases with a double-ring structure- Adenine and Guanine.

Pyrimidines

Bases with a single-ring structure- Thymine and Cytosine.

Complementary Pairing

Association between specific nitrogenous bases of nucleic acids stabilised by hydro bonding (A=T, C=G, U=A).

Antiparallel Strands

Describes the structure of DNA, two strands parallel to each other going in opposite directions (3'-5' and 5'-3').

Histone Proteins

A simple protein bound to DNA, involved in the coiling of chromosomes.

Nucleosomes

Bead-like structures formed by histones and DNA.

Super-coiled

A double helix of DNA that has undergone additional twisting in the same direction as or in the opposite direction from the turns in the original helix.

Plasmids

Small circular DNA molecules that replicate separately from the bacterial chromosome.

Recessive Gene

A gene that is expressed only in the absence of a dominant gene.

Chromosomes

A threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

Phenotype

The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

Genotype

An organism's genetic makeup, or allele combinations.

Alleles

Different forms of a gene.

Hybrid

An organism that has two different alleles for a trait.

Homozygous

Having two identical alleles for a particular gene.

Heterozygous

An organism that has two different alleles for a trait.

Purebred

An organism that always produces offspring with the same form of a trait as the parent.

Pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

Heredity

The transmission of traits from one generation to the next.

Monohybrid Cross

A cross between two individuals, concentrating on only one definable trait.

Dominant Gene

A gene that is expressed in the offspring whenever it is present.

Autosomes

Non-sex chromosomes.

Carrier

A person whose genotype includes a gene that is not expressed in the phenotype.

Co-dominance

A condition in which both alleles for a gene are fully expressed.

Punnett Square

Diagram that can be used to predict the genotype and phenotype combinations of a genetic cross.

Eukaryotic Genome

-Genes are not densely packed

-Mostly organized as single transcription units

-Often contain introns

Diploid (2n)

An organism or cell having containing two copies of each chromosome.

Haploid (n)

An organism or cell having only one complete set of chromosomes.

Polypeptide

A polymer (chain) of many amino acids linked together by peptide bonds.

Exons

Expressed sequence of DNA; codes for a protein.

Introns (spacer DNA)

Noncoding segments of nucleic acid that lie between coding sequences.

Locus (Plural, loci)

A specific place along the length of a chromosome where a given gene is located.

Functional RNA

A RNA molecule that functions without being translated. Carries out a job in the cell as RNA. eg. mRNA, tRNA, rRNA

Structural Regions

Regions of chromosomes which contain highly repetitive DNA sequences that typically do not code for information but instead protect the ends of the chromosome (telomeres) or act as anchor points for sister-chromatids and the proteins that direct chromosomes segregation during cell devision (centromere).

Telomeres

Repeated DNA sequences at the ends of eukaryotic chromosomes.

Centromere

The region of the chromosome that holds the two sister chromatids together during mitosis.

Chromatids

Bodies of tightly coiled chromatin; visible during cell division- two chromatids bound at a centromere make a chromosome.

Metacentric Chromosomes

Have the centromere close to the centre of the chromosome with the p arms and q arms close to the same length.

Submetacentric Chromosomes

Have a centromere that is not in the center, so the p arms are clearly shorter than the q arms.

Acrocentric Chromosomes

Have the centromere at the top of the q arms, and there is little or no p arm material.

Telocentric Chromosomes

A chromosome with the centromere more or less at one end such that only one arm is visible.

Transcription

The organic process whereby the DNA sequence in a gene is copied into mRNA.

Translation

The organic process whereby genetic information coded in messenger RNA directs the formation of a specific protein at a ribosome in the cytoplasm.

Coding DNA

Sequences of a gene's DNA (exons) that are coded to produce a specific protein and are transcribed and translated during protein synthesis.

Non-coding DNA

Sequences of a gene's DNA (introns) that do not encode protein sequences. Some non-coding DNA is transcribed into functional non-coding RNA molecules while others are not transcribed.

Gene Expression

The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs.

mRNA

Messenger RNA; type of RNA that carries instructions from DNA in the nucleus to the ribosome.

tRNA

Transfer RNA; type of RNA that carries amino acids to the ribosome.

rRNA

Ribosomal RNA; type of RNA that makes up part of the ribosome.

Pre-mRNA

Precursor mRNA; the first strand of mRNA produced by gene transcription that contains both introns and exons.

Sliceosome

Large and complex molecular machine found primarily within the nucleus of eukaryotic cells which removes introns from a transcribed pre-mRNA.

Promoter Sequence

DNA sequences that define where transcription of a gene by RNA polymerase begins.

Helicase

An enzyme that untwists the double helix at the replication forks, separating the two parental strands and making them available as template strands.

DNA Polymerase

An enzyme that brings about the formation of a particular polymer, especially DNA or RNA.

RNA Polymerase

Enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription.

Codons

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.

Anticodon

A sequence of three bases of a tRNA molecule that pairs with the complementary three-nucleotide codon of an mRNA molecule during protein synthesis.

Polycystronic

A mRNA that codes for greater than 1 protein. eg. prokaryotes

Monocystronic

Each mRNA produces one specific protein (allows for more complexity and variation in gene pool). e.g.. eukaryotes

lacI

Encodes the lac repressor.

Lac Repressor

A DNA-binding protein which inhibits the expression of genes coding for proteins involved in the metabolism of lactose in bacteria.

Polycistronic

The coding pattern of prokaryotes, in which one mRNA may code for multiple proteins.

Transcription Factors

Collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription.

Regulatory Sequence

Any segment of DNA that is involved in controlling transcription of a specific gene by binding certain proteins.

MicroRNAs (miRNA)

A small, single-stranded RNA molecule, generated from a hairpin structure on a precursor RNA transcribed from a particular gene.

Epigenetic Modifications

Changes in cell inheritance that are not due to alterations in the sequence of DNA nucleotides.

Methylation

A chemical modification of DNA that does not affect the nucleotide sequence of a gene but makes that gene less likely to be expressed (gene silencing).

Acetylation

Of DNA and histones causes nucleosomes to loosen and spread apart.

Monozygotic (MZ)

Twins that develop from a single fertilized egg that then splits in half. These twins are genetically identical.

Homeotic Genes (Hox)

Genes with establish identity of each specific segments, determining the basic structure and orientation of an organism.

SRY Gene

The sex determining region of the Y chromosome in males. Encodes the testis-determining factor, which turns the primordial gonads into the testes.

Lac Operon

A gene system whose operator gene and three structural genes control lactose metabolism in E. coli.

Mutation

Change in a DNA sequence that affects genetic information.

Point Mutation

Gene mutation in which a single base pair in DNA has been changed.

Substitution

A mutation in which a nucleotide or a codon in DNA is replaced with a different nucleotide.

Deletion

A change to a chromosome in which a fragment of the chromosome is removed.

Insertion

A mutation involving the addition of one or more nucleotide pairs to a gene.

Inversion

When a segment of chromosome is reversed end to end.

Frameshift Mutation

Mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide.

Synonymous Mutations

Change the nucleotide sequence without changing the amino acid sequence.

Non-synonymous

A nucleotide mutation that alters the amino acid sequence of a protein.

Discordant Medical Conditions

Medical conditions which contradict each other.

Sickle Cell Anemia (SCA)

A genetic disorder that causes abnormal hemoglobin, resulting in red blood cells that assume an abnormal sickle shape and is caused by a non-synonymous substitution point mutation.

Cystic Fibrosis (CF)

A genetic disorder that is present at birth and affects both the respiratory and digestive systems and is caused by a non-synonymous deletion mutation.

Gametes

Reproductive cells.

Nondisjunction

The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.

Aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.

Spontaneous Mutation

A random change in the DNA arising from errors in replication that occur randomly.

Induced Mutagens

Mutations caused by an outside agent, a mutagen (eg. UV RADIATION).

Mutagens

A chemical or physical agent that interacts with DNA and causes a mutation.

Binary Fission

A form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size.

Interphase

The resting phase between successive mitotic divisions of a cell, or between the first and second divisions of meiosis. (Involves G1, S and G2 phases).