gene expression

transcription process

process where one DNA strand is used to create an RNA molecule that is an exact copy of the coding strand

• occurs in the nucleus

Transcription is the process where mRNA is made from the template strand of DNA in the nucleus.

translation process

process where genetic code carried by the mRNA is decoded at the ribosome to produce a specific polypeptide chain/protein

• protein is then used for cellular functions (e.g. making an enzyme)

mRNA

mRNA is “messenger” RNA and is the short single strand of RNA that is made off the template strand.

short - only a copy of a specific section of a gene

mRNA function

carries code from DNA in the nucleus to the ribosome in the cytoplasm

RNAs have many different functions e.g. mRNA function is to carry sections of this genetic information to the ribosome for protein synthesis.

tRNA

clover lead shap of RNA which carries an amino acid at one end and has an anticodon on the other end

tRNA is “transfer” RNA that is complementary to the mRNA.

tRNA funcrion

anticodons match up with the codon on the mRNA to ensure the correct amino acids are added to the polypeptide chain

physically linking specific amino acids to their corresponding codons on messenger RNA (mRNA) molecule

rRNA

found in ribosome along with proteins to complete ribosome structure

The Ribosome is the structure that “reads” the mRNA and, through the use of tRNA, adds amino acids that correspond to each codon on the mRNA until a stop codon is reached.

rRNA function

helps read the m RNA sequence during translation

translation process

The mRNA strand threads through the ribosome, which reads the sequence one codon at a time.

tRNAs carrying amino acids are matched to the mRNA sequence in order, with their anti-codons complementary to the codons.

The ribosome links the neighbouring amino acids together with peptide bonds to form a polypeptide chain.

The tRNA detaches (and is released to leave the ribosome and pick up a new amino acid and the ribosome moves along the mRNA to the next codon.

Translation finishes when the ribosome reaches a STOP codon.

the polypeptide chain is folded into a functional protein

polypeptide chain

The polypeptide chain is the name for the chain of Amino acids which will fold together to make a protein.

metabolic pathways

A metabolic pathway is a series of linked biochemical reactions controlled by enzymes. The pathway begins with a specific substrate, which is altered in a series of defined steps, where the product of the first reaction becomes the substrate for the next reaction.

Each reaction in the chain is catalysed by an enzyme.

In a metabolic pathway, one gene encodes one enzyme. Each enzyme can only catalyse one specific reaction due to its unique shape.

mutations in metabolic pathways

• Mutations in a gene for an enzyme can cause a metabolic pathway to end before it should.

• If the mutation causes the enzyme (a protein) change shape, or have an altered structure it may lose its function.

• The function of enzymes in metabolic pathways is to catalyse biological reactions (steps in pathway). The product of one reaction becomes the substrate for the next reaction.

• If one enzyme does not function, it disrupts the pathway, as the next substrate in the pathway cannot be made. This can also cause a build-up of the substrate for the non-functioning enzyme, which can be toxic.

transcription and trasnlation similarities and differences

Transcription and Translation are both required to build a polypeptide chain.

These two processes are similar because:

1. they use the complementary base pairing rule. In transcription it ensures the mRNA strand is a faithful transcript of the DNA sequence. In translation complementary base pairing is used to match the anti-codons to the mRNA codons.

2. both processes need a template to "read off", the DNA template strand for transcription, and the mRNA strand for translation.

Translation and transcription are different because:

1. transcription takes place in the nucleus, whereas translation happens in the cytoplasm.

why is transcription and translation needed

Both processes are needed because DNA can't leave the nucleus due to its size, and also to reduce the risk of it becoming damaged. Transcription is needed to carry the DNA message (via mRNA) to the ribosome in the cytoplasm.

Translation occurs in the cytoplasm as this is where the ribosomes and amino acids are located.

Without transcription the template strand could not be made into mRNA, so the instructions for making the protein would never reach a ribosome to be translated. Without translation, even if transcription occurred there would be no process by which the information in the mRNA strand could be translated into protein. For this reason both processes are required to build a polypeptide chain.

why dna cant leave nucleus

1. too big, doesnt fit through nuclear pores

2. very fragile and cytoplasm has a lot of potentially damaging substances which could harm the dna

structure of DNA

DNA is a double-stranded molecule made up of a phosphate, deoxyribose sugar, and nitrogen base. The nitrogen bases are A, T, G and C. It is a long molecule (2 m long).

structure of RNA

RNA is a single-stranded short molecule made up of phosphate, ribose sugar, and nitrogen bases A, U, G and C.

DNA function

DNA function is to hold (long term storage) the genetic information for the cell. The genetic information contains the instructions for development and function of living organisms.

mrna ?

mRNA is relatively short lived while dna is long lived - this is why cells continuously produce mRNA and not DNA

also because mRNA is in higher demand

Gene expression

Gene expression – information from one gene is used to synthesise a functional protein

difference between environmental factor and mutagen

Environmental factor can be an internal or external factor that affects the organism’s phenotype. Such as nutrient availability affecting height expression in plants / humans. It does not change the organism’s genotype.

Mutagen – is a substance or environmental factor (e.g. UV rays) that changes genotype / base sequence. For example UV rays cause mutations in skin cells DNA, resulting in melanoma / cancer. Royal jelly amount changes phenotype but not genot

ribosome

The ribosome is an organelle, which ‘reads’ mRNA bases in a code of three bases at a time.

codon

the sequence of three consecutive nucleotides on the mRNA strand.

Anti-codon

three consecutive bases on a tRNA molecule that is complementary to mRNA codon.

coding strand function

The coding strands’ function is to increase the durability of the DNA strand. It reduces the risk that the DNA can be damaged and, as well as this, in the event that the template strand is damaged, acts as a template for repairing enzymes. For example, if a base was removed from the template strand and in the opposite location on the coding strand there was an adenine base, enzymes will repair the template strand by inserting a thymine base (following the complementary base paring rule). The coding strand ensures that the code on the template strand is current, and thus the resulting amino acid chains and final protein(s) are correct.

template strand function

The template strand’s function is to provide the correct sequence of amino acids in the protein by being “read” by enzymes during transcription

substrate (precursore/intermediate)

A precursor / intermediates are starting molecules or molecules within a pathway that are required for the next step in a metabolic pathway.

precursor substrate is a compound that serves as a starting material (precursor) for a metabolic reaction and is specifically acted upon by an enzyme (substrate) to produce another compound or a series of compounds (products) in a biochemical pathway. 

intermediate substrate is a compound produced in one step of a metabolic pathway that acts as the substrate (starting material an enzyme acts upon) for the next reaction in that same pathway

A substrate is the specific molecule that an enzyme acts upon to catalyze a chemical reaction

final product

A final product in a metabolic pathway indicates the end of the pathway.

enzyme cayayst

one gene codes for one enzyme and each enzyme can only catalyse one reaction due to its unique shape

substrate

a substrate is a substance that an enzyme binds with to produce a product