Gene expression (3.0)

DNA

A polymer made up of a 5-carbon sugar, a phosphate group and 4 nitrogenous bases (adenine, thymine, cytosine, guanine) that holds genetic information

Chromosome

A DNA structure tightly coiled around proteins that has genetic information

Gene

A piece of DNA that codes for one specific protein

Allele

An alternative version of a gene

Genotype

The genetic makeup of an organism, or a particular trait

Phenotype

The physical expression of an organism’s genotype

DNA triplets

A sequence of three nitrogenous bases on the DNA strand that code for an amino acid

What is the connection between DNA and proteins?

DNA contains the genetic instructions to build proteins

What are the differences between DNA and mRNA?

Structure (double stranded DNA, single stranded mRNA), sugar component (deoxyribose, ribose), base (thymine, uracil), purpose (long term storage, temporary messenger)

mRNA

A complimentary copy of the DNA template strand

Transcription process

Transcription occurs in the nucleus. The purpose of transcription is to make mRNA copies of genes/DNA. These can then leave the nucleus ensuring that DNA does not have to, allowing the mRNA made can be used directly in translation. DNA does not leave the nucleus because it needs to be protected from damage and degradation and it’s too big to fit through the nuclear pores. Transcription begins with enzymes unwinding and unzipping the DNA double helix to expose the bases of a gene. Free RNA nucleotides then join onto the DNA template strand according to the base pairing rule of T-A, C-G, G-C, A-U and are linked together by RNA polymerase. When the gene is transcribed, the RNA polymerase detaches from the template strand, the two DNA strands bind back into the double helix and mRNA leaves the nucleus through the nuclear pores and goes to the ribosome, where translation takes place.

Translation process

Translation occurs at the ribosome (made of rRNA). The purpose of translation is to use the mRNA from transcription to synthesize polypeptide chains which can then be packaged/processed into useful proteins for cellular functions. Translation begins when the mRNA attaches to a ribosome. The ribosome reads the mRNA in sets of three bases (a codon). When the ribosome reads the START codon/AUG the tRNA with the complementary anticodon temporarily binds to the codon of the mRNA bringing with it the corresponding amino acid methionine. This starts the process of translation. The mRNA is continued to be read in codons with the corresponding amino acid being bonded to each other with peptide bonds, forming a polypeptide chain. This process continues until a STOP codon/UAA/UAG/UGA is read and the polypeptide is released.

Codon

A group of three bases on mRNA - complimentary to a triplet on the DNA strand. Codes for an amino acid, which is attached to a complimentary tRNA anticodon.

What are proteins made of?

A biological molecule of 20 possible amino acids held together by peptide bonds in a polypeptide chain.

How does folding effect the structure and function of a protein?

Folding transforms the primary shape of a protein into a specific 3D tertiary shape. The shape of a protein determines its ability to function.

Mutation

A permanent change to the base sequence of a gene

Substitution mutation

One or more bases have been changed - may have no effect on the amino acid that is coded for because of redundancy of the genetic code

Insertion mutation

One or more bases have been added - may cause a frameshift, which affects every triplet downstream of the mutation

Deletion mutation

One or more bases have been deleted - may cause a frameshift, which affects every triplet downstream of the mutation

Enzymes and substrates

Enzymes are proteins that speed up chemical reactions in living organisms without being consumed in the process. They lower the activation energy needed for a reaction to occur and are needed for metabolic processes. Each enzyme has a very specific active site designed to bind to a particular molecule called a substrate to create a product.

Metabolic pathway definition and explanation

A series of enzyme controlled reactions, where the products of the previous reaction become the reactants/substrate for the next reaction.

How do DNA and environment result in the phenotype of an organism?

DNA provides the genetic blueprint, while the environment influences how those genes are expressed to produce an organism’s phenotype.

Environmental factor

Any factor, abiotic or biotic, that influences living organisms.