DNA Structure and Replication

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Presentation transcript:

DNA Structure and Replication Biology SL – Melinda Ragsdale

DNA Structure – Review Composed of nucleotides that are complimentary Base pairs are Adenine – Thymine Cytosine-Guanine DNA Backbone made of repeating units of 5-carbon sugar and phosphate covalently bonded Strands held together by hydrogen bonds between base pairs

DNA Replication Replication is semi-conservative – DNA splits into two individual strands each becoming the template for the new strand. Many enzymes are involved in replication DNA Helicase – job is to unzip DNA DNA Polymerase III – links nucleotides together and acts as a proof-reader DNA ligase – links pieces of DNA together (specifically Okazaki Fragments which will be explained later) RNA Primase – a small, temporary piece of RNA that “primes” the location of replication DNA Polymerase I – removes the RNA primer

DNA Replication – The Basics DNA has two ends – the 5’ and 3’ 5’ end always starts with a phosphate while 3’ ends with the sugar Because the strands are complimentary, one strand always runs 5’ – 3’ while the other runs 3’ to 5’ DNA replication always occurs in a 5’ -3’ direction so one strand can be copied faster than the other Replication fork – the place where the DNA splits and replication is initiated

Leading and Lagging Strands Since DNA is copied in a 5’ – 3’ direction, one strand of DNA can be copied constantly. We refer to this as the leading strand. The reverse strand is also copied in a 5’-3’ direction but it is forced to do so in a disjointed manner. We refer to this as the lagging strand because the copying occurs at a much slower rate. Okizaki fragments – Small pieces of DNA that have been copied DNA Ligase – the enzyme that pieces these small fragments together into a single strand.

RNA AND PROTEIN SYNTHESIS Converting the blueprints into protein

Central Dogma of Genetics Reproduction requires the transmission of genetic information from parent to offspring Genes are discrete units of heredity that is coded by base pair sequences Genes code for amino acids Amino acids build proteins

How is RNA different from dna? RNA = RIBONUCLEIC ACID MADE UP OF NUCLEOTIDES (JUST LIKE DNA) SINGLE STRANDED INSTEAD OF DOUBLE MADE IN THE NUCLEUS DOESN’T STAY IN THE NUCLEUS LIKE DNA – IT MOVES INTO THE CYTOPLASM RNA copies DNA and helps make protein THYAMINE IS NOT IN RNA → REPLACED BY URACIL

THREE DIFFERENT TYPES OF RNA PRODUCED Ribosomal RNA (rRNA) – combines with protein to form ribosomes Transfer RNA (tRNA) – brings (transfers) amino acids to the ribosome for protein assembly. Messenger RNA (mRNA) – the instructions (order of assembly) of the protein to be made.

DNA TRANSCRIPTION TRANSCRIPTION – DNA IS USED AS A TEMPLATE TO MAKE mRNA Occurs in a 5’ – 3’ direction GENE – THE SECTION OF DNA THAT IS COPIED GENES CONTAIN CODES FOR SPECIFIC PROTEINS THAT CONTROL “TRAITS” IN THE HUMAN BODY

Sense vs Antisense Sense strand of DNA codes for a strand of protein but it is NOT copied by mRNA Antisense (or nonsense) strand acts as the template for mRNA Adenine pairs with Uracil (instead of Thyamine) Cytosine pairs with Guanine

TRANSCRIPTION THE PROCESS OF mRNA COPYING A SECTION OF DNA THAT SECTION OF DNA THAT IS COPIED IS A GENE GENES ALWAYS HAVE THREE PARTS: PROMOTER REGION – TELLS RNA POLYMERASE WHERE TO BEGIN CODING REGION – THE ACTUAL SECTION THAT IS COPIED DOWN TERMINATOR – TELLS RNA POLYMERASE WHEN TO STOP

RNA EDITING WHEN mRNA IS MADE, SOME PARTS ARE USEFUL WHILE OTHER PARTS NEED TO BE REMOVED INTRONS – PARTS OF THE GENE THAT ARE NOT USEFUL → THEY ARE REMOVED EXTRONS – USEFUL PARTS OF THE GENE

THE GENETIC CODE THE NUMBER AND ORDER OF AMINO ACIDS DETERMINE THE PROTEIN SIMILAR TO OUR ALPHABET AMINO ACIDS = LETTERS PROTEINS = WORDS CODON – THREE NUCLEOTIDES ON mRNA THAT SPECIFY WHICH AMINO ACID IS USED TO MAKE THE PROTEIN

TRANSLATION TRANSLATION – MESSGENER RNA USES tRNA AT THE RIBOSOME (rRNA) TO CREATE PROTEIN STEPS IN TRANSLATION RIBOSOME BINDS TO THE MRNA TRNA BRINGS THE CORRECT AMINO ACID TO THE RIBOSOME THE PROTEIN GETS ASSEMBLED ONE AMINO ACID AT A TIME

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