DNA: Nucleic Acids and Protein Synthesis

DNA Structure and Replication

What is DNA?

• DNA stands for deoxyribonucleic acid

• DNA determines the traits of organisms by determining the structure of proteins. – Think of it as a “blueprint”.

• The proteins carry out all of the work in the cell and essentially carry out all of the actions of life!

Where Do I Find DNA?

• Chromosomes are in the nucleus of every cell. • Chromosomes are made up of DNA. • Genes are pieces of DNA that contain the instructions for building a protein.

The Structure of Nucleotides

• DNA is made up of repeating nucleotide subunits.

• One nucleotide = phosphate group, sugar (deoxyribose), and one of four nitrogenous bases

The Structure of Nucleotides

• The four nitrogenous bases ultimately give the nucleotide its “identity”

– Adenine (A)

– Thymine (T)

– Cytosine (C)

– Guanine (G)

Purines- A, G Pyrimidines- T, C

The Structure of DNA

• DNA is made up of two strands of nucleotides coiled up into a double helix or “twisted ladder” shape

• The sugar and phosphate

creates the backbone of

the DNA molecule

The Structure of DNA

• The bases attach to the sugar on the DNA molecule and base pair to a partner with a hydrogen bond. This creates the “rungs” of the twisted ladder.

• The bases of one nucleotide strand will base pair to the bases on the other nucleotide strand

– A always pairs with T

– G always pairs with C

The Structure of DNA

T pairs with A C pairs with G Sugar and phosphate forms the “backbone” Order of the bases holds the information

The Importance of Nucleotide Sequences

• The order of the bases holds the genetic information as a “code” – Just like the letters of the alphabet make up words!

• Example: ATTGAC means something completely different than TCCAAA

• The more similar two organisms’ DNA sequences are, the more related the organisms are!

DNA Replication • All new cells (made by mitosis and meiosis) need

a complete copy of the DNA – This is completed during S phase of Interphase

• DNA must be copied so each cell can have its own

copy. – This process is called DNA replication.

semiconservative replication – the process in which the DNA molecule uncoils and separates into two strands. Each original strand becomes a template on which a new strand is constructed, resulting in two DNA molecules identical to the original DNA molecule.

Replication Animation: http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/micro04.swf::DNA%20Replication%20Fork

How DNA replicates

1. Enzyme breaks the bonds between the bases that holds the two strands together. This is called “unzipping” the DNA.

2. Another enzyme (DNA polymerase) assembles a complementary nucleotide chain for each original nucleotide strand. The newly added nucleotide strand is called the complementary strand.

3. At the end you are left with two identical copies of the DNA.

DNA Replication

Practice DNA Replication

1.) A T T G C T A G

T A A C G A T C

2.) G C T A T C G A C

3.) A G C T A C A A T C C A

Gene to Protein

Gene to Protein The Central Dogma

RNA • RNA and DNA are both nucleic acids that are made out

of nucleotides

• Three main differences: – RNA is single stranded; DNA is double stranded – RNA’s sugar is ribose; DNA’s sugar is deoxyribose – RNA contains uracil (U); DNA contains thymine (T)

Types of RNA

• There are three main types of RNA that carry out important roles in the cell:

1. mRNA – brings instructions from the DNA in the nucleus to the cytoplasm

2. rRNA – makes up part of the ribosome

3. tRNA – brings amino acids to the ribosome to build proteins

Transcription -The process in which a strand of mRNA is synthesized by using the genetic information found on a strand of DNA as a template. -RNA polymerase reads the complementary DNA strand and attaches complementary RNA bases. • Occurs in the nucleus • An RNA copy of a portion of DNA is made

• Happens similar to replication except:

– One strand of RNA (single-stranded) is made – RNA polymerase is the enzyme that carries out transcription – A pairs with U (rather than T) – G pairs with C

http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter3/animation__mrna_synthesis__transcription___quiz_1_.html

Practice Transcription

Complementary DNA strand - T A C G G A C T G A T T

mRNA strand -

Translation

-the process in which the mRNA molecules is decoded to produce a sequence of amino acids for protein synthesis

– mRNA is read in codons (groups of 3 bases)

– Each codon has a particular amino acid that goes with it

– The genetic code is universal; all organisms use the same code

Translation

• Occurs on the ribosomes in the cytoplasm

• mRNA is “read” by the ribosomes (either “free” in the cytoplasm or on the rough endoplasmic reticulum) and tRNA molecules bring amino acids to the ribosome to be assembled into a polypeptide chain

• Rough ER is responsible for transporting the newly synthesized proteins to the Golgi apparatus where carbohydrates are added to it and it is packaged in a vesicle for transportation to the cell membrane.

polypeptide chain- chain of amino acids joined together by peptide bonds • proteins are polypeptide chains folded into specific shapes

Translation

Translation Animation: http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter3/animation__how_translation_works.html

Practice Reading the Genetic Code

• What amino acid is coded for by the following codons? – CCC

– GUA

– AUC

– AUG

– UAA

• What codons stand for serine?

Practice Transcription and Translation

Using the following DNA sequence, transcribe it into mRNA and then translate it into an amino acid sequence:

Coding DNA: A T G T T T A C C T A T G A C T A A

Complementary DNA: T A C A A A T G G A T A C T G A T T

mRNA:

amino acid

sequence :

Start, Phe, Thr, Tyr, Asp, Stop