Unit 2.1: BASIC PRINCIPLES OF HUMAN GENETICS

OVERVIEW OF THE CELLULAR BASIS OF LIFE Is the building blocks of life 50 to 100 Trillion About 2.5 billion at hand 200 types Each type has different functions

CELL THEORY A cell is the basic structural and functional unit of living organisms. The activity of an organism depends on the collective activities of its cells. According to the principle of complimentary, the biochemical activities of cells are dictated by the relative number of their specific sub-cellular structures. Continuity of life has a cellular basis

What is DNA? BACKGROUND INFO SLIDE – What is DNA? DNA is a long molecule that encodes our genetic instructions. (Our bodies are made up of around 50 trillion (50 x 1012) cells. Most of these cells contain a person’s genetic information within a long molecule called DNA (deoxyribonucleic acid). This DNA contains the genetic information that we inherit from our parents). DNA has a distinctive helical shape, like a twisted ladder. Two strands of DNA are twisted together into the double helix shape. (Our DNA is made up of specific sequences of letters or bases that encode instructions on how to make proteins. These bases [Adenine (A), Guanine (G), Cytosine (C) and, Thymine (T)] are lined up along two strands of DNA). The rungs of the ladder are called base pairs. The order of these bases make up the genetic instructions for making molecules in the body. These base pairs can break, allowing the sides of the helix to unravel. This special property is what allows DNA to copy itself, and to act as the instructions.

What is DNA? DNA stands for Deoxyribonucleic acid DNA is the genetic material of all living things on the planet It is found in the nucleus of your cells DNA holds the instructions to make all things in your body work properly. Each consisting of deoxyribose sugar, a phosphate group, and nitrogen- containing base A double helix, a ladderlike molecule that is coiled into a spiral staircase shape. The upright parts of the DNA ladder are alternating phosphate and sugar units, and the rungs of the ladder are made of pairs of nitrogen-containing bases.

DNA

DNA

The Bases: the chemical building blocks of DNA Adenine (A) Guanine (G) Thymine (T) Cytosine (C)

Purine bases: 5 carbons, 4 nitrogen Adenine (A) Guanine (G)

Pyrimidine bases: 5 carbons, 2 nitrogen Cytosine (C) Thymine (T)

Base Pairs Each of the bases have a partner they pair off with. Adenine (A) always partners with Thymine (T) Cytosine (C) always partners with Guanine (G)

Functions of DNA Replication Metabolism From one generation to another -> inheritance From cell to cell division Metabolism - Gene expression and protein synthesis (transcription, translation)

DNA REPLICATION Definition: is the process of making a copy of itself. [existing strands of DNA serve as templates (pattern) for building a new strand of DNA] Function: to produce more cells for growth and repair processes. Occurs during the (S) synthesis phase of the cell cycle, before a cell divides. This process has three steps (see next slide).

3 Steps in Replication STEP 1- Unwinding and Strand Separation DNA helicase break the hydrogen bonds between base pairs and unwind the helix. As the strand separate, replication forks form STEP 2- Adding Complementary Bases - DNA polymerase forms the new DNA molecule by traveling along each single strand and adding complementary nucleotides. Nucleotides are added to the exposed nitrogen bases. It follows base pairing rules (A- T and C- G) STEP 3- Formation of Two Identical DNA Molecules - The DNA winds back up producing 2 identical DNA molecules each consisting one new strands.

Enzymes involves during replication!

Helicase An enzyme needed for DNA replication A protein that works to “unzip” the DNA and separate the antiparallel strands to facilitate replication of each strand consistent with the semiconservative model of DNA replication.

Polymerase Reads the DNA strands from 3’ to 5’ (so builds DNA from 5’ to 3’) Brings in complimentary nucleotides (bases) Proofreads its work Replaces primer with DNA nucleotides When an incorrect base pair is recognized, DNA polymerase reverses its direction by one base pair of DNA.

Primase is an enzyme involved in the replication of DNA. This enzyme is the first to act once the replication bubble begins. It adds about 10 RNA nucleotides to the point of origin in a 5’ to 3’ direction Why? DNA polymerase recognizes the primer, NOT the exposed nucleotides

Ligase “ligate” – means to tie together an enzyme that attaches 2 pieces of DNA together. It forms covalent bonds between the sugars and phosphates of the DNA backbones. How useful? if 2 different DNAs were cute with the same restriction enzyme, they will have matching sticky ends. DNA ligase can the be combine these two different DNA molecules into a single DNA. This hybrid DNA is called recombinant DNA

How does DNA control the cell? A cell’s DNA needs to change forms. DNA cannot leave the nucleus to give commands, so it needs to make a smaller copy of itself called RNA. RNA leaves the nucleus and is read by the ribosome. The ribosome then makes a protein. The protein is DNA’s command.

RNA has the instruction and can leave the nucleus

RNA (Ribonucleic acid) Carries out the instructions encoded in DNA Most biological activities are carried out by proteins.

Roles of RNA Messenger Messenger RNA carries the genetic information copied from DNA in the form of a series of 3 base code “word” of which specifies a particular amino acids

Roles of RNA 2. Transfer Transfer RNA (tRNA) is the key to deciphering the code words in mRNA. Each type of amino acids has its own type of tRNA which binds it and carries it to the growing end of a polypeptide chain if the next code word on mRNA calls for it. The correct tRNA with its attached amino acid is selected at each step because each specific tRNA molecule contains a three base sequence that can be base-pair with its complementary code word in the mRNA

Roles of RNA 3. Formation Ribosomal RNA (rRNA) associates with a set of proteins to form ribosomes. These complex structure, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains They also bind tRNAs and various accessory molecules necessary for protein synthesis. Ribosomes are composed of large and small subunit, each of which contains its own rRNA molecule or molecules.

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