the relationship between nucleic acids and proteins

unit 3

eukaryotic cells

more complex, defined nucleus, DNA in nucleus, membrane-bound nucleus and other membrane-bound organelles

nucleic acid

• two types: DNA and RNA

• nucleotide monomers

• CHONP = carbon, hydrogen, oxygen, nitrogen, phosphorous

organic polymers that store genetic information and provide the instructions for the synthesis of proteins produced within an organism.

organic = carbon and hydrogen bonded together.

In RNA, thymine nucleotide is replaced with uracil

nucleotide

• phosphate group

• 5 carbon pentose sugar (ribose in DNA)

• a nitrogenous base (A, G, C, U = RNA | A, G, C, T = DNA)

DNA

provides instructions for forming proteins, a polymer composed of two polynucleotide chains that coil around each other to form a polymer composed of two polynucleotide chains that coil around each other to form a double helix. deoxyribonucleic acid.

• deoxyribose sugar

• thymine + adenine

• double helix

• found in nucleus

triplet

DNA formation

• nucleotides link together to form strands through condensation polymerisation.

• nucleotides are joined together by phosphodiester bonds.

• the linkage of sugar and the phosphate group creates the ‘sugar phosphate backbone’

• two strands join together through complimentary based pairing.

• made of two polynucleotide chains

RNA

protein synthesis. carries genetic information that is translated by ribosomes into various proteins necessary for cellular processes. mRNA, rRNA, and tRNA are the three main types of RNA involved in protein synthesis.

• single stranded

• ribose

• uracil + adenine

• delivers the message from DNA to the ribosome to produce proteins

• origin molecule is nucleic acid

• found in the ribosome (rRNA), nucleus and cytoplasm (mRNA, tRNA)

mRNA

messenger RNA

• role is to carry genetic information from the DNA to the ribosomes for protein synthesis.

• pre-mRNA is synthesised during transcription

codon

tRNA

transfer RNA

• Delivers specific amino acids from the cytoplasm to the ribosome where they are joined to form a polypeptide chain.

• Carries amino acids.

anticodon

rRNA

ribosomal RNA

• rRNA + proteins = ribosomes

• the main structural component of ribosomes in a cell

• binding of mRNA and tRNA to accurate translation of codons.

• ribosomes are where mRNA is translated to produce a chain of polypeptides.

the genetic code

• protein production

• transcribed and translated

• grouping adjacent nucleotides into threes called:

DNA → triplet

mRNA → codon

tRNA → anticodon

universal (genetic code property)

the same codon codes for the same amino acid, regardless of species

unambigious (genetic code property)

every codon can only code for one amino acid.

degenerate (genetic code property)

multiple codons code for the same amino acids

non-overlapping (genetic code property)

each triplet codon is read independently, without overlapping from adjacent triplets or codons.

genetic expression

• a series of events which result in formation of functional gene products such as proteins or non-coding strands RNA

• makes it possible for living organisms to produce proteins and products, making it crucial for maintaining life

protein synthesis process

transcription

occurs in the nucleus

1. DNA unwinds and unzips itself.

2. RNA polymerase attaches to upstream promotor region of DNA template strand

3. DNA template strand is transcribed by polymerase. RNA polymerase catalyses the addition of free nucleotides

4. Free RNA nucleotides pair with exposed complementary base pairs;

   1. RNA: Guanine pairs with cytosine

   2. RNA: Uracil pairs with Adenine

URACAL REPLACES THYMINE

5. New strand is joined (condensation polymerisation) to produce pre-mRNA

RNA processing

occurs in the nucleus

only eukaryotic cells experience this.

addition of a 5’ methyl cap

addition of a poly-A tail

removal of introns

exons spliced together

AFTER THIS PROCESS, mRNA IS NOW KNOWN AS MATURE mRNA

translation

translated into a sequence of amino acids, resulting in a polypeptide chain

occurs in the ribosome

1. mRNA binds to ribosome

2. tRNA with the complimentary anticodon to the mRNA codon carries a specific amino acid to the ribosome

3. tRNA anticodons attach to complementary mRNA codons allowing specific amino acids to detach

4. The amino acids are joined by condensation polymerisation, via peptide bond (requiring energy), producing a polypeptide chain.

5. Polypeptide chain is released when the ribosome reaches a STOP code on the mRNA **THE STOP CODE IS NOT AN AMINO ACID

alternative splicing

• allows for a single gene to code for multiple proteins

• particular exons of a gene may be included within or excluded from the final mRNA produced from that gene

• this means exons are joined in different combinations leading to different (alternative) mRNA strands.

• allows human genome to synthesis many more proteins that would be expected.

promotor

• it is a binding site for RNA polymerase (an enzyme responsible for transcription)

• in eukaryotes, the promotor region has a sequence of bases known as the TATA box

termination sequence

represents a sequence of DNA that signals for the end of transcription.

operator

• serves as a binding site for repressor proteins, which can inhibit gene expression

• typically only found in prokaryotic cells

introns

• regions of non-coding DNA that do not contribute to the final protein

• removed during RNA processing

• only eukaryotic genes contain introns.

exons

• region of DNA coding which are transcribed and translated into the final protein

• eukaryotic and prokaryotic

gene regulation → eukaryotes

gene expression is highly controlled and can be regulated at transcription (nucleus) RNA processing (nucleus) and translation (cytoplasm).

transcription factors are proteins that can bind to the promotor in DNA.

gene regulation → prokaryotes

gene expression consists of only transcription and translation only occurs in the cytoplasm.

transcription and translation occurs almost simultaneously.

operons

• found in prokaryotes

• the expression of multiple structural genes controlled by a single promotor and operator

• these structural genes share a common purpose, therefore it is more efficient to translate and transcribe almost simultaneously for prokaryotic cells.

trp operon

• ambiguous

• only codes for one codon

• so it doesn’t waste energy

a series of gene within a certain species of bacteria that code for the production of the amino acid tryptophan.

the structural genes each encode and enzyme to form the biochemical pathway that assembles the amino acid of tryptophan

repressor protein

binds to the operator to prevent transcription of structural genes when tryptophan is available

attentuation

terminates transcription through the formation of terminator hairpin loops in mRNA transcripts of the leader region

structural gene

codes for something used in the cell, enzyme, protein channels, etc.

regulatory gene

controls the expression of other genes.

amino acids

all amino acids have a common structure with a central carbon atom bonded to 4 things:

• a hydrogen

• a carbolyx group

• an amino acid

• an R group

20 R groups.

polypeptides

a polypeptide chain is formed when amino acids link together to form a peptide bond when adjourning amino acids.

this process requires energy

a polypeptide chain can be alone or connected to function.

primary structure

• the sequence (or chain) of amino acids in a polypeptide chain

• peptide bonds hold amino acids in the correct order

secondary structure

• the shape of a polypeptide chain caused by folding and coiling

• determined by hydrogen bonds between the amine and carboxyl groups of different amino acids.

ALPHA HELIX

BETA PLEATED SHEETS

teritiary structure

• the overall 3D conformation/shape of the polypeptide held together by different bonds

• disulfide bonding which is stronger

• most proteins are fully functional at this level

quaternary structure

• two or more polypeptide chains joined to form a functional protein

• occurs when a protein is made up of two or more polypeptide chains joined together.