Biology WACE Units 3 & 4

Allele

One of various alternative versions of the same gene (at the same locus), distinguished by small differences in DNA sequence

Asexual reproduction

Process by which a single parent produces identical offspring without the process of fusion of gametes; usually via mitosis or binary fission

Sexual reproduction

From of reproduction in which offspring are produced from two parents by the fusion of male and female gametes to form a zygote

Autosome

One of the 22 homologous pairs of chromosomes that are not a sex chromosome

Bivalent

Structure consisting of two homologous chromosomes joined together during (during prophase I of meiosis)

Binary fission

Division of a cell into two cells without mitosis. A prokaryotic cell undergoes this to form two identical daughter cells, a form of asexual reproduction

Cell cycle

Ordered sequence of events in a cells life from when it was formed from a parent cell to its division

Cell division

The splitting of a cell into two functional daughter cells

Centriole

Minute rod-shaped organelle present in many resting cells, just outside the nuclear membrane. Helps make the spindle fibres for cell division. Two centrioles in each centrosome. Plants often do not have

Centrosome

Organelle containing pair of centrioles; duplicates during cell division (S phase). While the DNA is duplicating it moves to separate poles of the cell. Contains centrioles that produce spindle fibres

Centromere

Constricted region of a chromosome where spindle fibres attach, joining the two sister chromatids. Enables movement of chromosomes during cell division

Chromatid

Daughter strand of a duplicated chromosome attached to another chromatid by a centromere

Chromatin

Organised, loosely coiled complex of DNA and its proteins found eukaryote non-dividing cells. More compact than prokaryotic DNA

It supercoils to become chromosomes visible during cell division

Chromosome

Structure composed of DNA bound to histone proteins that contains arrays of genes carrying genetic information. Prokaryotes generally have one circular chromosome whereas eukaryotes have multiple linear chromosomes

Crossing over

Exchange of genetic material between maternal and paternal homologous chromosomes occurring during prophase I of mitosis. Non-sister chromatids ‘cross over’

Cytokinesis

Division of cytoplasm immediately after mitosis, meiosis I or meiosis II to create two separate daughter cells

Diploid (2n)

Cell or organism has a genome that contains two copies (a pair) of each chromosome, usually one from each parent

Haploid (n)

Cell or organism has a genome that contains one copy of each chromosome, or half the diploid number

DNA

The information-containing molecule present in all living things that contains constructions, written in a chemical code of nucleotides, for production of proteins by the cell, which determines characteristics of living things. This information is sufficient for the making and maintaining of an organism. DNA is the also the genetic material that passes this information onto the next generation.

Fertilisation

Fusion of haploid male and female gametes during sexual reproduction to produce a diploid zygote. The random union of gametes is known as random fertilisation

Gamete

Male or female reproductive(sex) cell, one of each time combine at fertilisation

Gene

A unit of heredity that transmits information from one generation to the next. It is a segment of DNA that codes for a polypeptide

Heredity

The study of inheritance; the transmission of characteristics from one generation to another

Heterosome

Non-identical chromosomes that pair up at meiosis, such as the X and Y

Histone

Protein around which DNA winds in eukaryotic cells to form a nucleosome

Homologous chromosome

A pair of chromosomes the same size and shape and has the same genes at the same locations

Interphase

Stage between cell divisions that involves metabolic activity and growth; duplication of chromosomes and centrosomes; further growth and reproduction of organelles as cell prepares to divide

Karyotype

Standard graphical form to display and analyse chromosomes. Displays number and appearance of chromosomes of an organism or cell observed at metaphase

Locus

The position a gene occupies on a chromosome. Homologous chromosomes have genes at the same loci

Meiosis

A type of cellular division in sexually reproducing organisms that involves two rounds of cell division, but only one round of DNA replication. The chromosome number of a cell is halved so that the daughter cells are haploid to form gametes

Mitosis

Type of nuclear division in somatic cells that maintains the parental diploid number of chromosomes in the daughter nuclei. Basis for bodily growth and repair

Nucleotide

The basic building block of nucleic acids; nucleotides are linked together by phosphodiester bonds. Each nucleotide is made of a 5 carbon sugar, a phosphate group and a nitrogenous base (adenine, guanine, cytosine, thymine/uracil)

Nucleus

The organelle of eukaryotic cells that contains genetic material in the form of chromosomes and is enclosed by a nuclear membrane. In resting phase, genetic material is in the form of loosely coiled chromatin, in preparation for cell division it supercoils and condenses to form chromosomes

Sex chromosome

A chromosome that determines the sex of an organism and affects sexual traits

Synapsis

The pairing of homologous chromosomes during meiosis prophase I, at which point genetic material can cross over

Zygote

The first cell of a new individual; formed by fusion of male and female gamete (fertilisation) during sexual reproduction

Amino acid

An organic compound that is the building block of polypeptides or proteins. They are coded for by codons and carried to the ribosome by tRNA

Anticodon

Three consecutive nucleotides that is part of a tRNA molecule and is complementary to a codon

Coding DNA

Sections of DNA that code for a protein, they contain instructions that determine the order of the codons in mRNA which in turn determines order of amino acids in a polypeptide chain

Coding DNA are also called genes

Codon

A set of three consecutive nucleotides found in an mRNA molecule coding for a specific amino acids. They consist of four bases adenine, thymine, guanine and cytosine

Complementary base pairing

The phenomenon in which guanine always hydrogen bonds with cytosine (three hydrogen bonds); thymine always hydrogen bonds with adenine (two hydrogen bonds). Complementary pairing allows the helical structure

DNA helicase

An enzyme that helps the two strands of DNA unwind and ‘unzip’ separate, breaking the weak hydrogen bonds between nitrogenous bases

DNA ligase

An enzyme that seals fragments of nucleotides into a continuous polynucleotide strand by catalysing the formation of phosphodiester bonds

DNA polymerase

An enzyme that synthesises new strands of DNA in a 5’ to 3’ direction based on a template strand according to complementary base pairing rules attaching free nucleotides

They are important as they can make exact copies of fragments of DNA

DNA replication

Process a DNA molecule undergoes to make a complete and identical copy of itself readying a cell for cell division. It is a semi-conservative process as the two new strands consist of one parent strand and one replicated strand. Both contain exact copies of parent molecule genetic material

Double helix

Two linear strands that run opposite (antiparallel in the case of DNA) and twist together

Genetic code

Term used for the way that the four nitrogenous bases of DNA are ordered/sequence and contain info to direct the production of specific proteins

Genome

All the genetic material contained in an organism of cell. Contains the sequence of DNA in the chromosomes within organelles

Genome sequence

Sequence of all consecutive DNA nitrogenous bases spanning all the chromosomes of a cell from start to finish

Lagging strand

The strand synthesised discontinuously in small fragments known as Okazaki fragments in a 5’ to 3’ direction. RNA primers are attached at regular intervals and the strand is synthesised in these fragments between them. Moves away from the fork, hence must synthesise in short fragmentts

Leading strand

DNA strand synthesised continuously in a 5’ to 3’ direction moving toward the replication fork being unzipped

Mature mRNA

mRNA that has been processed after transcription, non-coding introns have been removed and remaining exons joined

mRNA

The RNA molecule that carries info from a gene to a ribosome for translation into a polypeptide

Non-coding DNA

All the DNA sequences within a genome that are not found within mRNA-coding exons. Examples include introns and promoters

Coding strand

Coding/non-template/sense strand, it has the same genetic code as the synthesised mRNA strand except uracil replaces thymine. It is not read in transcription. The template strand is its complement

Template strand

Template/non-coding/antisense strand of DNA is read by RNA polymerase to attach complementary base pairs. The mRNA complement of it produced in transcription is the same genetic code as coding strand except uracil replaces thymine

Okazaki fragment

Short fragment of DNA synthesised during DNA replication; multiple fragments are joined together to make the lagging strand during replication

Phosphodiester bond

Covalent bond that links a 3’ carbon in one sugar to a 5’ carbon in another sugar in DNA and RNA. Consists of a phosphate group and its covalent ester bond with the 3’ carbon and with the 5’ carbon. The bond connects nucleotides, which forms the backbone of DNA/RNA chain

Polypeptide

String of amino acids, joined by peptide bonds

Pre-mRNA

Strand of mRNA first produced after transcription of gene. Still contains introns

Promoter

Relatively short nucleotide sequence in the DNA of a gene to which RNA polymerase attaches to begin synthesis of mRNA in transcription, signalling where to begin

Protein

Type of essential biological macromolecule. Consists of one or more folded and modified polypeptides

Protein synthesis

Process whereby cells produce proteins from instructions encoded in genes. Involves processes of transcription and translation

Replication fork

Junction between unwound single strands of DNA and the intact double helix during DNA replication

Ribosome

An organelle found in all cells facilitating the interaction of mRNA and tRNA in transporting and connecting specific sequences of amino acids into polypeptides coded for by mRNA codons (translation)

Mostly composed of rRNA, which binds to mRNA to form mRNA-ribosomal complex; facilitates forming of peptide bonds between amino acids

Transcription

Synthesis of mRNA in which the sequence of nucleotides is complementary to the sequence in stored DNA template strand code. It is the same as the coding strand except uracil replaces thymine

Translation

Synthesis of a polypeptide using the information in mRNA. RNA nucleotide code translated into an amino acid sequence with each codon coding for a specific amino acid

Triplet

Set of three consecutive nucleotides in DNA

tRNA

An RNA molecule that contains an anticodon (complementary to mRNA codon). It carries an amino acid specified by the codon to the ribosome during protein synthesis. The amino acid is removed when anticodon binds to the codon and is added to polypeptide chain