DNA, Protein Synthesis and Epigenetics

created particularly for the human biology investigation in term 3, week 2.

give the definition of a gene

A segment of a DNA molecule with a coded set of instructions in its base sequence for a specific protein product; when expressed, may determine the characteristics of an organism

give the definition of a chromosome

´A tightly coiled section of the DNA molecule that is only visible just before and during cell division

What are the similarities between nuclear and mitochondrial DNA?

• Both have the nitrogenous bases (A,T,C,G)

• Double stranded structure

• both utilise the process of transcription, translation, etc.

What are the differences between nuclear and mitochondrial DNA?

Nuclear:

• found in nucleus

• numerous genes

• genes code for different characteristics

• double helix structure (chromatin + chromosome)

• is wrapped around histone protein (tangled network chromatin, chromosome while dividing)

Mitochondrial:

• found in the cytoplasm, the mitochondria

• 37 genes (24- code for tRNA + rRNA molecules, other 13 code for enzymes for cellular respiration)

• circular in shape

Describe the structure of the ribosome:

• Mass- 60% rRNA, 40% protein

• 2 Subunits- smaller for mRNA, larger for forming peptide bonds between amino acids = create peptide chains

• has binding sites for both mRNA and tRNA

• found on the ER, or free floating in cytoplasm

Describe the process of transcription

1. chemical messengers enter the nucleus from the cytosol, binding to the DNA at the relevant gene

2. Helicase unwinds and seperates the DNA into 2 seperate strands, usually separating around 17 base pairs

3. RNA polymerase transcribes one strand of DNA to form a complementary molecule of RNA. this is one strand.

4. a sequence of bases near tthe end of the gene signal to the RNA polymerase to stop copying, thus releasing the molecule.

5. the mRNA is released.

6. the mRNA contains junk sequences, which must be removed. these are called introns, and after their removal, the remaining bases (exons) are linked together. the final product is a strand consisting of sequence of codons, which is a triplet of bases, which will translate into polypeptides.

7. the mRNA molecule leaves the nucleus and enters the cytoplasm, to a ribosome.

8. transcription also doesn’t occur all the time. there is an active repressor, and once binded to an operator, transcription is prevented.

Describe the process of translation

The mature mRNA molecule leaves the nucleus and enters the cytoplasm, where it binds to a ribosome (composed of a small and large subunit).

The ribosome attaches to the mRNA at the start codon (AUG) which codes for the amino acid methionine

´The ribosome moves along mRNA one codon at a time

´In translation, tRNA molecules act as the interpreters of the mRNA codon sequence.

´At the middle of the folded strand of tRNA nucleotides there is a tight loop. This loop contains a three-base coding sequence called the anticodon.

´Each tRNA anticodon is complementary to a codon on the mRNA and carries the corresponding amino acid.

´The ribosome attaches the correct tRNA anticodon with its amino acid, to the codon on that section of mRNA.

´The ribosome moves along to the next codon on the mRNA. The correct tRNA for that codon brings its amino acid to join with the first amino acid that is there from the previous tRNA.

´The first tRNA is released to pick up more amino acids

´The ribosome continues along the mRNA until the whole chain is read and all the amino acids are attached.

´ATP supplies the energy to form bonds between each amino acid.

How does an epigenome change during the lifetime ?

1. Fertilisation: the reprogramming of parental genomes, and many histone modifications

2. During Pregnancy:the diet of the mother during pregnancy affect the DNA methylation, increasing likelihood of illness

3. During early Development: new tads guide cell specialisation

4. Middle age: DNA methylation begins to decrease

5. As you age: epigenome changes, tag patterns degrade resulting in higher risk of disease

what are the factors cause epigenetic tags to be added or removed from an epigenome?

1. diet: a diet rich in folate, omega 3 fatty acids, whole grain foods and vitamin b-12 affect DNA methylation (off/ on) adds tags

2. stress: produces long lasting impacts/ sudden changes. this can cause long lasting silencing due to metyhlation (DNA)

3. exercise: regular exercise induce changes in histone aceyltation and DNA methylation

4. environmental exposures: pollutants, toxins, smoking can effect dna methylation and cause other histone modifications

What is the start codon?

AUG

What are the stop codons?

UAG, UAA, UGA

What is an essential amino acid? What is their function? How many?

• cannot be created by the body, must be found in food.

• 9

• their function: building muscle, regulating immune function,

• enzyme and protein synthesis

What is an non-essential amino acid? What is their function? How Many?

• 5

• these can be created by our body

• protein synthesis

• many specialised roles such as detoxification and neurotransmission

What is an semi- essential amino acid? What is their function? How many?

• these are amino acids that are not neccessary unless there is illness,, stress or other issues.

• these can be created by the body, but often supplements or foods containing the acids must be intaken when there isn’t enough

• 6

where can essential, non essential and semi-essential amino acids be found?

essential:

• in food

Non essential:

• can be produced by our bodies and other metabolic processes

Semi-essential:

• supplements, food

• can be created by body

give the examples of essential amino acids (4)

• lysine

• methionine

• valine

• Leucine

• tryptophan

• threonine

• phenylalanine

• histidine

• isoleucine

give examples for non essential amino acids (3)

• alanine

• asparagine

• aspartic acid

• glutamic acid

• serine

give examples for semi essential acids (3)

• arginine

• cysteine

• glutamine

• glycine

• proline

• Tyrosine

give the 3 types of RNA

• mRNA

• tRNA

• rRNA

what is the purpose of mRNA?

• formed in nculeus

• long strand of RNA nucleotides complementary to one gene of a strand of DNA

what is the purpose of tRNA?

• transfer RNA

• responsible for interpreting the codon present on mRNA

• Small molecule of RNA, containing only 70–90 nucleotides.

• Each tRNA molecule is able to carry a specific amino acid o the ribosome where proteins are made. 

What is the purpose of rRNA?

• rRNA and protein = ribosome

• ensures the allignment (correct) between ribosome, tRNA molecule and the mRNA molecule

• Has an enzymatic role in the formation of peptide bonds between amino acids.

Antibody

• degend body againstantigen/ foreign invaders

• travels through bloodstream and enables them to identify and defend against bacteria

• antibody, immunoglobin

Contractile protein

• responsible for muscle contraction and movement

• actin and myosin

enzymes

• biological catalysts

• they convert substances, are used in metabolic reactions and to degrade substances

• amalyase, lipase, protease

Hormonal protein

• messenger proteins that help co-ordinate certain bodily functions

• growth factors, cortisol, testosterone

structural protein

• protect the structure of animal body and maintains it

• collagen

storage protein

• reserve amino acid until necessary

• Ferritin

Transportation

• carrier proteins, move molecule from one place to another

• haemoglobin

what is epigenetics?

´Epigenetics refers to changes in gene expression that result from mechanisms other than changes in the genes (DNA).

what is epigenome?

´Their epigenome is the sum of all the factors that determine when, where and which genes are ‘switched on’ or expressed.

what is gene expression

´process of copying information from DNA onto mRNA, then translating the message into a series of amino acids to form a protein

DNA methylation

methyl-based molecules attached to some cytosine bases

´Stops the gene from being “seen”

´Causes genes to be switched off

histone modification- acetylation

´acetyl group to the histone protein.

´ changes the shape of the histone and how the DNA is wrapped around them.

´This opens up the DNA sequence and exposes more DNA to transcription/translation

´Increases likelihood of gene expression

´acetyl group = promotes transcription

no acetyl group= does not promote/ restrains transcription

histone modification- methylation

´methyl-based molecules attach to histones.

´Can increase OR decrease gene expression

´Effect on gene expression depends on where the methyl groups attach and how many attach