Biology - Unit 6 Transcription and Translation_The Genetic Code

central dogma of molecular biology

• It outlines the process through which DNA is transcribed into RNA, which is then translated into protein.

• The key components of the central dogma are:

  1. DNA replication

  2. Transcription

  3. Translation

the genetic code

• Refers to the sequence of nucleotides in DNA and RNA that determines the amino acid sequence of proteins.

• Nearly universal across all living organisms, meaning that the same codons (sequences of three nucleotides) specify the same amino acids across nearly all living organisms, from bacteria to plants to animals.

difference between DNA and RNA

• DNA is double stranded, RNA is single stranded

• DNA has deoxyribose sugar, RNA has ribose sugar

• DNA contains thymine, RNA contains uracil instead of thymine.

transcription

When RNA polymerase synthesizes new mRNA.

• It creates RNA antiparallel to the template DNA strand.

• Cased on complementary base pairing and hydrogen bonding.

• Original DNA strand isn’t changed; needs to be stable.

translation

The process of building polypeptide chain of building a polypeptide chain of amino acids, guided by the sequence of codons on the mRNA.

mRNA

• A single stranded molecule that transmits genetic information from DNA to ribosomes, where proteins are synthesized.

• It is formed during the process of transcription, where a specific segment of DNA is copied.

• It contains codons

tRNA

• The site of the 3-base sequence that ‘recognizes’ and matches up with the codon on the mRNA molecule.

• It is based on complementary base pairing rules

• There is a specific of it and anticodon for each type of codon.

amino acid

• Molecules that serve as the building blocks of proteins, linked together by peptide bonds during translation.

essential amino acids

• 9 of the 20 amino acids that can’t be synthesized in human cells and must be obtained from food sources in your diet.

• Valine

• Leucine

• Isoleucine

• Tryptophan

• Phenylalanine

• Lysine

• Histidine

• Methionine

• Threonine

mutations

Gene mutations are random changes in a sequence of DNA, which in turn can impact protein structure and function.

somatic (body) cells

• Mutations are not passed on to offspring, but could be passed on to replicated cells

• Could lead to loss of function or development of cancerous cells

germ (sex) cells

• Mutations are potentially passed on to offspring, and all of their cells will be affected.

• Could be beneficial or harmful (in the case of genetic disease)

base substitutions

A single base is substituted by another:

• silent

• mis-sense

• non-sense

frame shift mutations

Insert or deletion of one or more nucleotides

• insertion

• deletion

silent mutation

• If the third base in a tripled had been substituted, the resulting amino acid may not be altered (due to degeneracy in the genetic code)

mis-sense mutation

• Results in the substitution of one amino acid for another

• The resulting protein may be non-functional or have reduced function

nonsense

• A single base is substituted by another which results in a codon that codes for “STOP”

sickle cell mutation

• Involves the substitution of one base for another in the HBB gene, causing a single amino acid to be altered.

frame shift mutation

• A single base is inserted or deleted, shifting the reading sequence for al l those after it.

• The resulting protein will be very different from the original (it is most likely to be non-functional)

degneracy

• Refers to the redundancy in the genetic code, where multiple codons can specify the same amino acid.

protein denaturation

• Involves the disruption of the non-covalent interactions (such as hydrogen bonds, ionic bonds, and hydrophobic interactions) that maintain the protein’s shape and structure.

• The primary amino acid sequence remains intact完整, but the secondary, tertiary, and quaternary structures are altered.

potential caused of protein denaturation

1. Temperature

   • Elevated temperatures can disrupt the hydrogen bonds, ionic bonds, and hydrophobic interactions that maintain a protein’s structure.

2. pH changes

   • Alterations in pH can affect the ionization of amino acid side chains, disrupting ionic bonds and hydrogen bonds within the protein.

3. Various chemicals

   • Certain chemicals can interact with the protein, disrupting its folding and stability.

consequences of protein denaturation

Functionality loss:

• Denatured proteins often lose their functionality, as their active sites may no longer be properly shaped to bind substrates or perform their biological roles

• This can affect enzymatic activity, structural integrity, and cellular processes.

reversibility of protein denaturation

Some protein can refold and regain their functional structure if the denaturing conditions are removed (reversible denaturation), while others may remain permanently denatured (irreversible denaturation.