BioNinja Notes- Genetics

Central Dogma

The flow of genetic information within living organisms from DNA to RNA to proteins.

DNA

The genetic blueprint of a cell, organized into instructions (genes) that encode specific traits.

RNA

A temporary photocopy of a gene, made via transcription, which is sent to ribosomes.

Proteins

Molecules synthesized by ribosomes via translation, carrying out encoded cellular functions.

mRNA

Messenger RNA, the transcript copy of DNA that encodes the protein sequence.

tRNA

Transfer RNA, which carries amino acids to the mRNA transcript for assembly.

rRNA

Ribosomal RNA, provides catalytic activity for combining amino acids.

Transcription

The process of copying a DNA sequence into complementary RNA sequences by RNA polymerase.

Gene Expression

The process coordinated by transcription factors that determines the transcription and activity of genes.

Transcription Factors

Proteins that mediate or impede the binding of RNA polymerase to the promoter, switching genes on and off.

Proteome

The totality of proteins expressed within a cell or organism at a specific time.

Translation

The process of synthesizing proteins from mRNA sequences, resulting in a polypeptide chain.

Amino Acids

Building blocks of proteins, linked together by peptide bonds in a specific sequence.

Start Codon

A specific codon (AUG) that signals the initiation of translation.

Stop Codon

A codon that signals the termination of translation.

Genetic Code

The set of rules that determine which amino acid corresponds to each mRNA codon.

Point Mutations

Changes to a single base within the DNA code, which may affect protein production.

Frameshift Mutations

Mutations caused by the insertion or deletion of nucleotides, altering the reading frame.

Block Mutations

Changes to segments of a chromosome, leading to alterations in large segments of DNA.

Epigenetics

The study of changes in gene expression that do not involve alterations to the underlying DNA sequence.

Methylation

An epigenetic modification where a methyl group is added to DNA, often reducing transcription.

Alternative Splicing

A process by which different combinations of exons are joined, producing different polypeptides from a single gene.

Gene Regulation

The mechanisms controlling the expression levels of genes at the genomic, transcriptomic, or proteomic levels.

Monozygotic Twins

Twins that develop from a single fertilized egg, sharing the same genome but differing due to environmental factors.

What is the role of DNA in the central dogma?

DNA serves as the genetic blueprint that contains the instructions for encoding specific traits.

How is RNA produced according to the central dogma?

RNA is produced through the process of transcription, where a gene's DNA sequence is copied into a complementary RNA sequence.

What are the main functions of proteins in living organisms?

Proteins carry out various cellular functions as determined by the information encoded in mRNA.

What are ribosomes?

Ribosomes are cellular structures that synthesize proteins by translating the mRNA sequence.

What is the significance of the central dogma in biology?

The central dogma explains how genetic information flows from DNA to RNA to proteins, essential for cellular function.

What are the three main types of RNA involved in protein synthesis?

Messenger RNA (mRNA), Transfer RNA (tRNA), and Ribosomal RNA (rRNA).

What is the function of messenger RNA (mRNA)?

mRNA is the transcript copy of a DNA instruction that encodes the protein sequence.

What is the role of transfer RNA (tRNA) in protein synthesis?

tRNA carries amino acids to the mRNA transcript for assembly into proteins.

What does ribosomal RNA (rRNA) contribute to protein synthesis?

rRNA provides the catalytic activity needed to combine amino acids during protein synthesis.

What is transcription?

Transcription is the process of copying a DNA sequence into complementary RNA sequences by RNA polymerase.

What role does RNA polymerase play in transcription?

RNA polymerase binds to the promoter, separates the DNA strands, and synthesizes RNA by aligning free RNA nucleotides with their complementary DNA bases.

Where does transcription occur in eukaryotic cells?

Transcription occurs in the nucleus of eukaryotic cells.

What happens at the terminator sequence during transcription?

At the terminator sequence, the synthesised RNA transcript is released, and the double helix of DNA reforms.

What is the promoter in transcription?

The promoter is a DNA sequence that signals RNA polymerase where to begin transcription.

What happens to the hydrogen bonds during transcription?

The hydrogen bonds between base pairs in the DNA are broken, allowing the strands to separate.

What type of bonds are formed between RNA nucleotides during transcription?

Covalent bonds are formed between the sugar-phosphate backbone of the RNA nucleotides.

What is the purpose of transcription?

The purpose of transcription is to produce an RNA transcript that carries the genetic information necessary for protein synthesis.

Base Pairing in RNA Transcription

The RNA transcript has a sequence complementary to the DNA template, as DNA bases form hydrogen bonds with specific RNA nucleotides.

Adenine and Uracil Pairing

Adenine pairs with uracil via two hydrogen bonds during RNA transcription.

Guanine and Cytosine Pairing

Guanine pairs with cytosine via three hydrogen bonds during RNA transcription.

Importance of Base Pairing in Transcription

Base pairing ensures the RNA transcript is a correct and reliable copy of genetic instructions.

What are transcription factors?

Proteins produced by regulatory genes that mediate or impede the binding of RNA polymerase to the promoter, helping to switch genes on and off.

What is the role of activator proteins in gene expression?

Activator proteins bind to enhancer sites to increase transcription rates.

What is the function of repressor proteins in gene expression?

Repressor proteins bind to silencer sites to decrease transcription rates.

How can the presence of transcription factors affect cells and tissues?

Certain transcription factors may be tissue-specific, contributing to the differentiation of cells and tissues.

What influences the activity of transcription factors?

Chemical signals such as hormones can moderate the activity of transcription factors, altering gene expression patterns.

What is epigenetics?

The study of changes in organisms due to variations in gene expression levels without alterations to the underlying DNA sequence.

What is cell differentiation?

Cell differentiation is the process by which a less specialized cell develops into a more specialized cell type, activating specific genes to produce distinct proteins.

What is a genome?

The genome is the totality of DNA sequences (both genes and non-coding DNA) within a cell or organism.

What is a proteome?

The proteome is the totality of proteins expressed within a cell or organism at a specific time.

How do different cell types arise from the same genome?

Different cell types arise from the same genome by selectively activating different genes, leading to the production of distinct proteins that define their morphology and function.

What is the role of mRNA in translation?

mRNA carries the genetic information from DNA to the ribosomes, where it is translated into a sequence of amino acids.

What is a codon?

A codon is a triplet of bases in mRNA that codes for a specific amino acid according to the genetic code.

What is the function of tRNA in protein synthesis?

tRNA transports specific amino acids to the ribosome and matches them with the corresponding codon on the mRNA via its anticodon.

What bonds are formed between amino acids during translation?

Peptide bonds are formed between amino acids during translation, catalyzed by the ribosome.

How does the ribosome function in translation?

The ribosome reads mRNA sequences in codons, facilitates the binding of tRNA, and catalyzes the formation of peptide bonds between amino acids to produce polypeptides.

What role do anticodons play in translation?

Anticodons on tRNA pair with complementary codons on mRNA to ensure the correct sequence of amino acids during polypeptide synthesis.

Ribosome Structure

Ribosomes are composed of two distinct subunits: a small subunit and a large subunit, each made of protein and rRNA.

Function of Small Subunit

The small ribosomal subunit binds to mRNA and reads it in triplets known as codons.

Function of Large Subunit

The large ribosomal subunit contains binding sites for two tRNA molecules, each carrying a specific amino acid.

Role of Ribosome in Translation

The ribosome transfers amino acids between tRNA molecules, sequentially growing a polypeptide chain as it moves along the mRNA.

tRNA Release

Once a tRNA molecule has transferred its amino acid to the growing polypeptide chain, it is released to collect another amino acid.

Initiation of Translation

Translation begins when the ribosome reaches a start codon (AUG), establishing the reading frame for mRNA.

Termination of Translation

Translation ends when the ribosome encounters a stop codon, signaling the end of the polypeptide synthesis.

Polypeptide Growth

The ribosome sequentially adds amino acids to the growing polypeptide chain as it translates the mRNA sequence.

Translation Efficiency

Multiple ribosomes can translate a single mRNA sequence simultaneously, increasing the efficiency of protein synthesis.

What is the genetic code?

The genetic code is the set of rules that determines which amino acid corresponds to each mRNA codon.

What does universality refer to in the context of the genetic code?

Universality means that almost every living organism uses the same genetic code, with some rare exceptions in viruses.

What is degenerate coding in the genetic code?

Degenerate coding means that some codons can code for the same amino acid, allowing for redundancy in the genetic code.

How many codons are in the genetic code?

There are 64 codons in the genetic code.

How many standard amino acids are coded by the genetic code?

The genetic code corresponds to 20 standard amino acids.

Genetic Code Representation

The genetic code is typically represented as a codon table that shows which codons correspond to which amino acids.

What are codons and anticodons?

Codons are triplets of bases in mRNA that define a specific amino acid, while anticodons are complementary triplets on tRNA that pair with codons during translation.

How do codons and anticodons interact?

Codons on mRNA are recognized by complementary anticodons on tRNA, ensuring correct pairing for protein synthesis.

What is the significance of complementary pairing in translation?

Complementary pairing between codons and anticodons ensures that sequences are accurately translated into the correct amino acids.

What bases pair between codons and anticodons?

In RNA, adenine pairs with uracil, and guanine pairs with cytosine during codon-anticodon pairing.

What is an example of codon-anticodon pairing?

A codon with the sequence AUG corresponds to an anticodon with the sequence UAC.

How can changes in nucleotide sequences lead to genetic diseases?

Altered nucleotide sequences can change protein structure, potentially leading to loss of function and disease conditions.

What is sickle cell anaemia?

Sickle cell anaemia is a genetic disease caused by a mutation affecting the gene coding for haemoglobin, altering the amino acid sequence from glutamic acid to valine.

What is the consequence of the mutation in sickle cell anaemia?

The mutation leads to the formation of insoluble fibrous strands of haemoglobin, altering red blood cell shape and function, leading to anemia.

What amino acid change causes sickle cell anaemia?

The change from glutamic acid (Glu) to valine (Val) due to the mutation alters hemoglobin structure, resulting in sickle-shaped red blood cells.

How does sickle-shaped red blood cells affect their survival?

Sickle-shaped red blood cells are destroyed more rapidly than normal cells, leading to lower red blood cell counts and anemia.

What is a gene mutation?

A gene mutation is a change in the nucleotide sequence of a section of DNA encoding for a specific trait.

What are alleles?

Alleles are different versions of a gene that arise from mutations.

What is the difference between germ line mutations and somatic mutations?

Germ line mutations occur in gametes and can be passed to offspring, whereas somatic mutations occur in body cells and cannot be inherited.

Do mutations in non-coding DNA affect traits?

Mutations in non-coding DNA typically do not influence an organism's characteristics unless they impact gene expression levels.

What is the role of mutations in genetic diversity?

Mutations contribute to genetic diversity by creating new alleles that change observable features of organisms.

Sources of Mutation

Mutations can arise from errors during DNA replication or exposure to mutagenic agents.

DNA Replication Errors

Proofreading errors during DNA replication can lead to gene mutations if incorrectly paired nucleotides are not corrected by DNA polymerase.

Mutagenic Agents

Mutagens are agents that induce permanent changes in DNA, increasing mutation rates.

Physical Mutagens

Physical mutagens include forms of radiation such as X-rays and UV light that can damage DNA.

Chemical Mutagens

Chemical mutagens comprise substances like reactive oxygen species and certain metals (e.g., arsenic and alkylating agents).

Biological Mutagens

Biological mutagens are organisms like viruses (e.g., HPV) and bacteria (e.g., H. pylori) that can induce mutations.

What is a point mutation?

A point mutation involves a change to a single base within the DNA code, potentially altering the protein produced.

What are the types of point mutations?

The types of point mutations include silent mutations, missense mutations, and nonsense mutations.

What is a silent mutation?

A silent mutation is a DNA change that does not alter the amino acid sequence due to codon degeneracy.