What is the ultimate job of the cell?

TO MAKE PROTEINS!

THIS REQUIRES DNA AND RNA! AND…. THREE PROCESSES: REPLICATION TRANSCRIPTION TRANSLATION

NUCLEIC ACIDS DNA – DEOXYRIBONUCLEIC ACID RNA – RIBONUCLEIC ACID

DNA Deoxyribonucleic acid

DNA comes from chromosomes

DNA is made up of smaller units called nucleotides

Each nucleotide is made of 3 parts – a base, a sugar, and a phosphate

The sugar in DNA is deoxyribose hence the name of DNA

DNA BASES There are 4 possible bases: A for adenine T for thymine G for guanine C for cytosine

It’s like a CODE! The sequence of the nucleotide bases creates a “language” The only letters in this language are A T C and G

The Language of DNA Every three letters represents an amino acid. There are 20 amino acids. There are 64 possible ‘words’ that can be made from those 4 letters. Some of the ‘words’ represent an amino acid while others represent a period indicating a ‘stop’.

The nucleotide sequence The nucleotides are in order on purpose. A T T G C C is different from A T A G C G The sequence is a code. Information to make one protein

DNA scientist pioneers Watson and Crick – scientists in 1953 who discovered that DNA is made of two chains of nucleotides that are joined together at the nitrogen base by hydrogen bonds. Rosalind Franklin – discovered that DNA is made of two strands and that the sugar- phosphate molecules make up its backbone.

DNA scientist pioneers Together they showed that DNA is in the shape of a double helix

Central Dogma of Molecular Biology Information goes from DNA to RNA to proteins

Central Dogma of Molecular Biology The transfer of information from DNA can be seen in 3 processes: 1. DNA replication 2. transcription 3. translation

DNA Replication If a cell reproduces, then the DNA reproduces so it must be copied EXACTLY in order for a new cell to function. DNA replicates during S phase in Interphase

Step 1 The two strands of DNA unwind and separate like unzipping a zipper. Notice the nitrogen bases are exposed.

Complimentary Bases There are complimentary bases floating around. Each base has a compliment Adenine likes Thymine Cytosine likes Guanine

Step 2 The free bases floating around pair up with their complementary bases.

When DNA replicates, the bases form complementary pairs A pairs with T C pairs with G

Step 3 The sugar and phosphate parts bond together to form a complete new strand of DNA

DNA Polymerases are the enzymes that bond the new nucleotides together.

There is one old strand of DNA and one new strand of DNA. This is called semiconservative.

Example A section of DNA has a nucleotide sequence of A-T-T-G-C-C What would be the sequence that form the complement?

Practice G-C-C-A-T-A C-T-A-C-G-A T-C-T-A-G-A A-T-T-G-A-C

Central Dogma of Molecular Biology Information flows from DNA to RNA to proteins.

This is called Transcription All DNA is in the nucleus of a cell, however, the proteins are made OUTSIDE the nucleus. Something has to carry that information from the nucleus to the ribosome (where the proteins are assembled.

RNA does this job. It contains ribose sugar instead of deoxyribose.

There are three types of RNA made in transcription: messenger RNA (mRNA) transfer RNA (tRNA) ribosomal RNA (rRNA)

Transcription Transcription copies the instructions in the DNA onto a strand of messenger RNA (mRNA)

DNA is unwound and a complimentary strand of mRNA is made

Transcription The same as replication EXCEPT: the sequence is copied to messenger RNA (mRNA) A pairs with Uracil (U) instead of T mRNA is a SINGLE strand. NOT a double strand.

CHANGE! RNA pairs A with U (Uracil) NOT Thymine (T)! A pairs with U C still pairs with G There is NO ‘T’ in RNA

Transcribe the following sequence from DNA into mRNA G-C-A-T-T-A-C-G-A

Once a strand of mRNA is made, the code or instructions to make a protein can be read.

Every set of three letters in the mRNA bases is called a codon.

Each codon represents either one amino acid or gives the “STOP” instruction.

There are 4 codons- which allows for 64 possibilities.

Translation (reading the sequence) Now that transcription has occurred, translation is the process that will build proteins (the last of the central dogma DNA – RNA – Proteins)

Translation Ribosomes are the source of protein synthesis in the cytoplasm of the cell

mRNA has been made and is in the cytoplasm. Translation can now begin to build proteins.

The ribosomal RNA (rRNA) attaches to the mRNA and starts to ‘read’ the sequence three bases at a time.

Another form of RNA called transfer RNA (tRNA) carries the amino acids to the ribosomes. tRNA has a sequence called an anticodon that pairs with the codons. Example: if the mRNA codon is A-U-C then the tRNA anticodon is U-A-G Process repeats until a STOP Codon appears

Sequence of events Amino acid attaches to tRNA tRNA carries amino acid to rRNA rRNA ‘sits’ on top of mRNA and reads the sequence tRNA anticodons match with mRNA strand Protein is formed by the matching Translation stops when ‘stop codon’ appears