DNA STRUCTURE AND REPLICATION What is DNA DNA

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DNA STRUCTURE AND REPLICATION

DNA STRUCTURE AND REPLICATION

What is DNA? �DNA stands for Deoxyribonucleic acid �It is a double helical shape-

What is DNA? �DNA stands for Deoxyribonucleic acid �It is a double helical shape- or like a twisted ladder �Found in the nucleus of all of your cells �Codes for every thing that is you! Hair colour, eye colour how tall you are etc. �Made up of molecules- called Nucleotides �It is the organisation of the nucleotides that makes DNA a double helix

Nucleotide structure �Nucleotides have a sugar /phosphate backbone-like the edge of the ladder �And

Nucleotide structure �Nucleotides have a sugar /phosphate backbone-like the edge of the ladder �And the “rungs” made of complimentary nitrogen rich bases Adenine (A) Thymine (T) Guanine (G) Cytosine (C) All have different chemical structures so they can only match up or “pair” up in one way- COMPLEMENTARY BASE PAIRING (A-T) AND (C-G)

DNA STRUCTURE DNA BASES SUGAR/PHOSPHATE BACKBONE

DNA STRUCTURE DNA BASES SUGAR/PHOSPHATE BACKBONE

CHROMOSOMES � In the nucleus of each cell, the DNA molecule is packaged into

CHROMOSOMES � In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times. � Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope. � Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms. ” � The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.

More about the Chromosome…. . Diagram of a chromosome

More about the Chromosome…. . Diagram of a chromosome

And more!!! � In the body cells, humans have 46 chromosomes, made up of

And more!!! � In the body cells, humans have 46 chromosomes, made up of 23 pairs. There are 44 chromosomes numbered 1 -22 (called autosomes) according to size from the smallest to the largest and two sex chromosomes: X and Y ( see the booklet and text book) � Women’s chromosomes are described as 46 with an XX; men’s as 46 with an XY �The chromosomes are long strands of genes � Since the chromosomes come in pairs, the genes also come in pairs � In each of the approximate 20, 000 genes there is a piece of genetic information which guides our growth, development and health and is in the form of a chemical code, called the genetic code � The genetic code in the DNA, is virtually identical across all living organisms and is like a recipe book for the body to make proteins

Genes…. �Different genes are active in different cell types, tissues and organs, producing the

Genes…. �Different genes are active in different cell types, tissues and organs, producing the necessary specific proteins; some genes are ‘switched off’ and others are ‘switched on’ �Changes to the genetic code can mean that a particular protein is not produced properly, produced in the wrong amounts or not produced at all…this can be because of things called carcinogens or things which can cause mutations in the genetic code…. to produce the wrong things � In some cases, the change in the genetic code can result in a genetic condition, affecting our growth, development and how our bodies work –(we look at some conditions when we do genetics specifically)

Here’s the story…

Here’s the story…

DNA Replication �So…we know what DNA is and what chromosomes and genes are…. .

DNA Replication �So…we know what DNA is and what chromosomes and genes are…. . we look next at cell division and how we get the genes we do! BUT �We need to look at a process called replication which MUST happen before there is any information to be available to be passed on from parents to children or from one cell to another…. �This process is part of the cell cycle and happens just before division…the cell cycle is covered a little next year and in year 12 Biology

DNA REPLICATION �The process starts with one double-stranded DNA molecule and produces two identical

DNA REPLICATION �The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule. �Each strand of the original double-stranded DNA molecule serves as template for the production of the complementary strand, a process referred to as semiconservative replication. Cellular proofreading and error checking mechanisms ensure near perfect fidelity (or accurate copying) for DNA replication.

Replication Continued �In a cell, DNA replication begins at specific locations in the genome,

Replication Continued �In a cell, DNA replication begins at specific locations in the genome, (or points on the DNA) called "origins". � Unwinding of DNA at the origin, and synthesis (MAKING) of new strands, forms a replication fork. �Enzymes are responsible for “un-zipping” the DNA. . bringing the nucleotides to match or complementary binding with the template strand then “zipping” back up the DNA strand.

Replication…. �There is a leading and lagging strand of DNA…this means where the ‘copying

Replication…. �There is a leading and lagging strand of DNA…this means where the ‘copying starts’ �So when the DNA has been split or separated one of the template strands is copied in one direction, while the other is copied in the opposite way…. the lagging strand is more difficult and has to be rejoined in short pieces �The following diagram is more complex than you need but shows this well

Replication http: //www. youtube. com/watch? v=zd. Dki. Rw 1 Pd. U&feature=related

Replication http: //www. youtube. com/watch? v=zd. Dki. Rw 1 Pd. U&feature=related