Genetics Exam 3

Codon

Encode the information for a specific amino acid in a protein

Transcription

The transfer of genetic information from the base sequence of DNA to the base sequence of RNA, mediated by RNA synthesis

(same language, slightly different form [two strand DNA to one strand RNA])

Translation

Conversion of information encoded in the nucleotide sequence of an mRNA molecule into the linear sequence of amino acids in a protein

(different language [RNA to protein])

Messenger RNA (mRNA)

A single-stranded complimentary copy of the nucleotide sequence in a gene

Ribosomal RNA (rRNA)

RNA molecules that form part of the ribosome

Ribosomes

Cytoplasmic particles composed of two subunits that are the site of protein synthesis

Transfer RNA (tRNA)

A small RNA molecule that contains a binding site for a specific type of amino acid and a three-base segment known as an anticodon that base-pairs with the codon in mRNA

Promoter

The region of a gene on a DNA molecule to which RNA polymerase binds and initiates transcription

R Group

Each amino acid having a different side chain that can be positively, negatively, or neutrally charged

Peptide Bond

A covalent chemical link between the carboxyl group of one amino acid and the amino group of another amino acid

Amino Acid

Subunits of polypeptides (also subunits of proteins since proteins are polypeptides folded into a 3D structure)

Polypeptide

A molecule made of amino acids (an amino acid chain) joined together by peptide bonds

Anticodon

A group of three nucleotides in a tRNA molecule that pairs with a complementary sequence (codon) in an mRNA molecule

Prion

A protein folded into an infectious conformation (shape) that is the cause of several disorders including Mad-cow disease

The central dogma of molecular biology

DNA transcribes to mRNA which is translated into protein

Three Stages of Transcription

1.) RNA polymerase binds to a promoter in the DNA along with regulatory proteins (initiation) 2.) RNA polymerase moves along the DNA unwinding it, and as it does, it links RNA nucleotides into a strand of RNA in the order specified by the base sequence of the DNA (elongation) 3.) The RNA polymerase reaches the end of the gene, and the completed mRNA strand is released (termination)

Three Stages of Translation

1.) The initiation complex is formed by the combination of mRNA, initiation RNA, and the small ribosome subunit 2.) The ribosome moves along the mRNA, linking amino acids and producing a growing polypeptide chain (elongation) 3.) The polypeptide is released from the ribosome and undergoes a conformational change to produce a functional protein

Levels of Protein Structure

Primary: the amino acid sequence in a polypeptide chain (one dimensional)

Secondary: the pleated or helical structure in a protein molecule brought about by the formation of bonds between amino acids (two dimensional)

Tertiary: the 3D structure of a protein molecule brought about by folding on itself

Quaternary: the structure formed by the interaction of two or more polypeptide chains in a protein (hemoglobin)

Chromatin Remodeling

A process of chemical changes to DNA and histones that activate and inactivate gene expression; these complexes generally restrict access to promoters which RNA polymerase attaches to during transcription

DNA Methylation

A mechanism that the cell uses to silence gene expression, which is associated with genome imprinting, cancer, and how we make barr bodies

RNA Interference (RNAi)

A mechanism of post-transcriptional gene regulation that regulates gene expression through the action of micro RNAs and blocks expression of a gene

Protein

The end product of gene expression which is an essential component of all biological structures and processes that impact cell structure, metabolism, hormonal response, cell-to-cell signaling systems, and the immune system

Enzyme

Proteins that facilitate biochemical reactions in the cells (they make things happen)

Substrate

The specific compound acted on by an enzyme (the thing we start with that the enzyme will do something with to change it in some way)

Product

The specific compound that results from enzymatic action

Metabolism

The sum of all biochemical reactions by which cells convert and utilize energy (breaking down things to get energy or using energy to build things up)

Phenylketonuria (PKU)

An autosomal recessive disorder of phenylalanine metabolism that’s caused by phenylalanine levels and the products of secondary reactions; it can result in intellectual disabilities if untreated, and there is a dietary treatment containing phenylalanine that should be maintained for life

Galactosemia

A genetic disorder caused by lack of an enzyme (GALT) in sugar metabolism that is heritable and associated with the inability to metabolize the sugar galactose; it can cause cataracts and intellectual deficiencies if left untreated

Somatic Mutation

Mutations that occur in cells of the body that don’t form gametes and not transmitted to future generations

Germ-Line Mutation

Mutations that occur in cells that produce gametes and inherited by future generations

Mutagen

Environmental agents like radiation and chemicals that cause mutations

Nucleotide Substitutions

Swaps one nucleotide for another causing one codon to be different which will change one amino acid

Frameshift Mutations

A number of bases (other than multiples of three) that are added to or removed from DNA causing a shift in the codon reading frame

Allelic Expansion

An increase in gene size caused by an increase in the number of trinucleotide sequences

Influences on mutations rates

The size of the gene (larger genes have higher mutation rates), nucleotide sequence (presence of nucleotide repeats are associated with higher mutation rates), and spontaneous chemical changes (C/G base pairs are more likely to mutate than A/T pairs)

Examples of environmental factors that can cause mutations

Radiation, UV light, tobacco smoke, and some pesticides

Examples of mutations caused by chemicals

Base analogs (mutagenic chemicals that structurally resemble nucleotides and are incorporated into DNA or RNA during synthesis), modification of bases (some chemical mutagens directly modify he bases in DNA, changing one base to another), and intercalating agents or chemicals that insert themselves into DNA (produce frameshift mutations by distorting the double helix or resulting in addition or deletion of a base pair during DNA replication)

Three Types of Nucleotide Substitutions

Missense mutations—cause the substitution of one amino acid for another in a protein (same length)

Sense mutations—mutations in a single nucleotide which can change a termination codon into one that codes for an amino acid, producing elongated proteins (longer length)

Nonsense mutations—an amino acid specifying a codon changing to one of three termination codons, producing shorter proteins (shorter length)

Benign Cancer

Non-invasive cancer cells

Metastatic Cancer

Cancer cells that are invasive and spread to other sites

Tumor Suppression Genes

Encode proteins that suppress cell division and regulate the cell cycle, and the deletion or inactivation of these products cause cells to divide continuously

Proto-oncogenes

Genes that initiate or maintain cell division and may become cancer genes (oncogenes) by mutation

Two main properties of cancer

Uncontrolled cell division and the ability of these cells to spread to other sites in the body

Metastasis

The ability of cancer cells to spread to other sites in the body

The typical progression of cancer

Begins in a single cell then one cell does mitosis and makes a cell identical to it, and the cell accumulates specific mutations over a long period of time; once cancer cells escape control of the cell cycle, they divide continually, causing mutations to continue to accumulate

How tumor suppression genes and proto-oncogenes regulate the cell cycle

Tumor suppression genes decrease cell division by suppressing cell division at control points in the cell cycle while proto-oncogenes increase cell division by initiating or maintaining cell division

What happens when tumor suppressor genes and proto-oncogenes are not functional

If proto-oncogenes are mutated, they can become cancer genes called oncogenes which are permanently turned on proto-oncogenes that cause uncontrolled cell division.

If tumor suppression genes are deleted or inactivated, then cells divide continuously

What happens when cancer metastasizes

Cancer cells break away from their original tissue and become attached to the wall of a blood or lymph vessel, secreting digestive enzymes to create an opening. Then, they cross the wall at the breach causing cancer cells to creep along inside blood vessels and leaving the bloodstream the same way they got in, starting new tumors in new tissues

The difference between sporadic and inherited cancers

Inherited cancers are inherited mutant genes that cause a predisposition to cancer while sporadic cancers are caused by accumulation of a number of mutations in somatic cells which is the most common

Cloning

The production of identical copies of molecules, cells, or organisms from a single ancestor

Restriction Enzymes

Bacterial enzymes that cut DNA at recognition sites

Vectors

Self-replicating DNA molecules used to transfer foreign DNA segments between host cells

Plasmids

Little circles of DNA that comes from bacteria

Polymerase Chain Reaction (PCR)

Amplification of DNA segments rather than an entire molecule that consists of multiple cycles of in vitro DNA synthesis

Gel Electrophresis

Separates DNA fragments based on size by having DNA fragments migrate through a gel from a negative pole to a positive pole using an electric charge

DNA Sequencing

A technique for determining the nucleotide sequence of a fragment of DNA

How nuclear transfer for cloning is performed

An egg and its surrounding cumulus cells are removed from the ovary before the cumulus cells are separated from the egg and the nucleus is removed by microsurgery. Then, the cumulus cell nucleus is injected into an egg that’s implanted into a surrogate mother

DNA cloning requirements

Cut DNA into reproducible fragments using restriction enzymes, paste DNA fragments into a carrier molecule for transfer into host cells, and grow host cells to obtain large quantities of cloned DNA to study

DNA cloning steps

DNA is cut with a restriction enzyme, and the fragments are mixed with vector molecules cut by the same enzyme before plasmid vectors with inserted DNA fragments are transferred into bacterial cells to replicate and produce many clones of the recombinant DNA molecule

Three steps of PCR

1.) Denaturation—DNA is heated to break the hydrogen bonds between the two polynucleotide chains

2.) Annealing—short nucleotide sequences are mixed with the DNA and bind to complementary regions on single-stranded DNA

3.) DNA Synthesis—the heat-stable enzyme Taq polymerase is added to synthesize a complementary DNA

Goal of PCR

For DNA to be amplified without having to be purified and can be present in small amounts, and it’s faster than other methods

Alternative Splicing

Using different combinations of exons from the same gene to make different proteins, allowing us to express one gene in multiple different ways which increases diversity

The effects of nucleotide substitution

Ranges from no change to catastrophic change

If this changes a codon for an amino acid into a stop codon, or changes a stop codon into one for an amino acid, that will change length of the polypeptide chain leading typically to big effects

Uracil base pair

Uracil & Adenine (Uracil replaces Thymine)