D1.2 Protein synthesis

Protein synthesis

Define transcription.

List the roles of RNA polymerases in the process of transcription.State the complementary base pairing utilized in transcription.

Distinguish between the sense and antisense strands of DNA.

Protein syntehsis: DNA» RNA» Polypeptide chain of amino acids

transcription»transation»modifications

Transcription- syntehsis of RNA useing DNA as a template; copying of DNA sequence into RNA

RNA polymerase:

• promoter-binds to a site on the DNA at the beginning of a gene

• unwinds DNA double helix and separates into 2 strands

• bring nucleotides with complemantary base to the template strand ; A-U; G-C

• covalently joins nucleotide sugar-phosphate to form contionous; strand generating mRNA transcript of DNA sequence

Antisense strand- template strand

Sense strand-coding strand

Outline how stability of the information stored in DNA is maintained

Single DNA strands can be used as a template for transcribing a base sequence, without the DNA base sequence changing. In somatic cells that do not divide, such sequences must be conserved throughout the life of a cell.

DNA strands are only parted for a short time so bases are only briefly vulnerable to chemical change; stability ise ssential cuz they may be transcribed multiple times

Define gene expression. Outline the major steps of gene expression. State that the pattern of gene expression is how cells differentiate for specific functions. Outline the role of transcription in regulating gene expression.

Gene expression- overall process where information carried by gene is used to make proteins/rna molecules that has observable effects on an organism; transcription and translation

pattern of gene expression is how cells differentiate for specific functions. Cell differentiation- cell specialization into diff. taks / functions

Limit to understanding that not all genes in a cell are expressed at any given time and that transcription, being the first stage of gene expression, is a key stage at which expression of a gene can be switched on and off.

Define translation. State the location of translation in cells.

Outline the roles of mRNA, ribosomes and tRNA in translation.

Describe the structures of mRNA and tRNA. Describe the structure of the ribosomes, including the small and large subunits and the names and roles of the tRNA binding sites.

translation- synthesis of polypeptide chain from mRNA in cytoplasm. The base sequence of mRNA is translated into the amino acid sequence of a polypeptide.

• mRNA has a site to which ribosome can bind and sequence of codons that specify the amino acid sequence of polypeptide; has start and stop codon

• tRNA- anticodon 3 bases at one end and amino acid on the other end; translates base sequence of mRNA; have anticodon that corresponds to codon in mRNA; brings correct amino acid

• ribosomes-small and large subunit; small subunit is where mRNA attaches and large subunit is where 3 tRNAs can simultaneously bind and has catalytic site the makes peptide bonds

Explain the reason that a sequence of three nucleotides is required to code for the 20 amino acids commonly utilized by organisms. Define codon, degenerate and universal as related to the genetic code.

1 base and 2 base combinations can’t code for 20; thats why 3 bases is used; can code for 64 combinations

genetic code is universal- almost all organisms use the same genetic code;the e set of rules used by living cells to translate information encoded within genetic material into proteins

codon= sequence of three bases on mRNA that code for a specific amino acid

notable features of the genetic code: degeneracy & universality

degenarate- cuz different codons can code for the same amio acid

universal- cuz almost all living organisms use the same code with only minor changes

movement of ribosome along mRNA

1. initiation

2. elongation and translocation- ribosome moves one codon at a time towards 3’ end of mRNA; catalyzing bonds between amino acids brought by tRNA making a polypeptide chain

3. termination

Define point mutation.

Explain how point mutation may affect protein structure using an example.

Define gene mutation. State the cause of sickle cell anemia, including the differences in the HbA and HbS alleles. State the difference in RNA sequences in the transcription of the HbA and HbS alleles. State the difference in amino acid sequences in the translation of the HbA and HbS alleles. Outline the consequences of the HbS mutation on the structure and function of the hemoglobin protein. Discuss the symptoms of sickle cell disease. (?)

Point mutation-a change in a single nucleotide in the DNA sequence: single base pair is added, deleted or changed.

• Causes SNP = single nucleotide polymorphism, new forms of gene which differ by single bases here and there.

A point mutation is Effect on Protein Structure

Point mutations can lead to changes in amino acids, potentially altering protein structure and function. For example, a mutation in the hemoglobin gene can change glutamic acid to valine in its sixth codon, affecting hemoglobin's ability to carry oxygen.

gene mutation- is a permanent alteration in the DNA sequence of a gene.

Cause of Sickle Cell Anemia

Sickle cell anemia is caused by a point mutation in the Hb (beta-globin) gene, resulting in the HbS allele. The HbA allele (most humans have) encodes normal hemoglobin, while HbS encodes a variant that causes red blood cells to become sickle-shaped.

Differences in RNA Sequences

The RNA sequence for HbA is UAC (coding for glutamic acid), while for HbS, it is UAU (coding for valine) as its sixth codon.

Differences in Amino Acid Sequences

HbA has glutamic acid, whereas HbS has valine at the sixth position of the beta-globin chain.

Consequences of HbS Mutation

The HbS mutation leads to hemoglobin polymerization under low oxygen conditions, causing red blood cells to deform, leading to blockages in blood vessels and reduced oxygen delivery.

Symptoms include pain crises, anemia, fatigue, swelling, and increased risk of infections.