Biology Unit 4 Topic 1

Deoxyribonucleic Acid

Thread like chain of nucleotides carrying the genetic instructions of an organisms in a double helix of antiparallel strands

Nucleotides

Organic molecules that are the building blocks of DNA; made up of deoxyribose sugar, phosphate group and nitrogenous bases that make up a sugar phosphate backbone and nitrogenous bases.

Double Helix

A pair of helices would around a central axis; the shape of a DNA molecule

What are the Nitrogenous bases of DNA (Deoxyribonucleic Acid)

Adenine (A), Thymine (T), Guanine (G), Cytosine (C)

What are the nitrogenous bases of RNA (ribonucleic acid)

Adenine (A), Uracil (U), Guanine (G), Cytosine (C)

Leading strand

The exposed strand of an unwound DNA molecule that runs in the 5’ to 3’ direction towards the replication fork

Lagging strand

The exposed strand of an unwound DNA molecule that runs in the 3’ to 5’ directions away from the replication fork.

Daughter Cells

The Two cells produced after a parent cell undergoes cell division

DNA Helicase

The enzyme responsible for breaking the hydrogen bonds between nitrogenous bases to unwind the DNA double helix into separate strands.

DNA polymerase 

The enzyme responsible for matching and binding free-floating nucleotides to exposed nucleotides on unwound DNA strands.

Semi-conservative replication

Replication of DNA resulting in two copies that each contain one of the original strands and one new strand.

Sister Chromatids

The original and replicated chromosome joined by a centromere after DNA replication.

Replication fork

The point of a DNA molecule where the helicase enzyme breaks hydrogen bonds between nitrogenous bases and exposes the two strands of DNA.

Mitosis 

The process by which cells replicate during growth in multicellular organisms and reproduction in unicellular organisms.

Gametes

Reproductive cells in sexually reproducing organisms

Alleles

Different forms of the same gene found at the same locus in the genome of a species

Haploid Cell

A cell that contains a single set of unpaired chromosomes, such as the 23 chromosomes in a human sperm or egg cell.

Meiosis

The process by which haploid sperm and egg cells (gametes) are made from a diploid parent cell

Diploid cell

A cell that contains two complete sets of chromosomes, one set inherited from each parent.

Parent Cell

The original cell that divides to produce new cells, called daughter cells.

Crossing Over

The transfer if genes between homologous chromosomes during prophase I in meiosis.

Meiosis II

Once the diploid germ cells have undergone crossing over and replication in Meiosis I, the process of creating haploid gametes (sex cells) can begin. In order to reduce the number of chromosomes by half, the steps of Meiosis I is repeated.

Spermatogenesis

begins when spermatogonia undergo mitotic division into diploid cells called spermatocytes. The diploid spermatocytes then undergo meiotic division resulting in four haploid spermatids.

Oogenesis

begins when oogonia undergo mitotic division into diploid cells called primary oocytes. The diploid primary oocytes then undergo meiotic division to become haploid secondary oocyte and a haploid polar body. The secondary oocyte progresses through meiosis II to produce an ovum during ovulation.

Gene expression

The sequence of steps from reading a segment of DNA (a gene), transcribing the sequence of nitrogenous bases to messenger RNA, translating the messenger RNA to a polypeptide chain and finally refining and modifying the structure of the polypeptide chain to produce a functional protein.

Genes

the molecular codes for physical and chemical characteristics of all living organisms.

Genome

The complete set of all gene-containing chromosomes an individual carries in its cell.

Codon

A series of three nitrogenous bases on an mRNA strand that will match with the anticodons on a tRNA molecule to determine amino acid selection.

Amino acid

The molecular building blocks of proteins.

Translation

Reading of an mRNA strand by a ribosome to form a polypeptide chain from amino acids.

RNA

Ribonucleic acid- a single stranded molecule of genetic information essential for protein synthesis.

Transcription

The process that occurs in the nucleus of eukaryotic cells. It allows single-stranded Messenger NRA (mRNA) molecules to be produced from a double-stranded DNA molecule. [      ] can be broken into three stages: Initiation, Elongation, Termination

Initiation

RNA polymerase is assisted by transcription factors as it unzips the DNA double helix by breaking the Hydrogen bonds between bases. This exposes the bases, allowing them to bind with free-floating nucleotides in Elongation.

Elongation

RNA polymerase begins to produce an mRNA strand. THe DNA strand acts as a template, which the RNA polymerase moves along adding corresponding nucleotides though complementary base pairing. New nucleotides are added to the 3’ end of the growing mRNA strand since synthesis occurs in the 5’ to 3’ direction. Synthesis of mRNA follows the same base pairing of AT GC, however Thymine is replaced by Uracil.

Termination

A stop codon signals the RNA polymerase to cease transcription and terminate the mRNA molecule

Translation

Ribosomes in the soma of a eukaryotic cell build a polypeptide chain from amino acids by translating mRNA codons. This is called [ ]

Initiation (Translation)

A ribosomal subunit attaches itself and moves along an mRNA strand in the 5’ to 3’ direction until it recognizes a start codon (AUG). A free-floating transfer RNA (tRNA) molecule with the anticodon UAC carrying methionine attaches to the mRNA start codon. The ribosome is now ready to begin translating the mRNA into a polypeptide chain.

Elongation (Translation)

As ribosome progresses along mRNA strand reading codons and matches them with the anti codon of nearby tRNA molecules. As each tRNA anticodon binds with its corresponding mRNA codon it releases its amino acid which joins the growing polypeptide chain through a condensation polymerization reaction.

Terminaion (translation)

The process of elongation continues until the ribosome reads a stop codon and releases the polypeptide chain into the cytoplasm of the cell.