Wk 4 Biomedical Science PT 1

Describe Transcription (Protein Synthesis Pt1)

The process by which DNA is copied into mRNA. It has 3 main steps:

1) Initiation: 

• An enzyme called RNA polymerase binds to the promoter (a special DNA sequence that signals the start of a gene). 

• The DNA strands unwind, and one strand (the template strand) is used to make RNA. 

  2) Elongation: 

  • RNA polymerase moves along the DNA, reading the template strand and building a complementary mRNA strand. 

  • Instead of thymine (T), RNA uses uracil (U), so A pairs with U instead of T. 

  • Example: If the DNA has TACG, the mRNA copy will be AUGC. 

  3) Termination: 

  • RNA polymerase reaches a termination signal (a specific DNA sequence that tells it to stop). 

  • The new mRNA strand is released. 

    DNA is a recipe book, and transcription is like writing down a copy of a specific recipe (mRNA). 

Describe Translation (Protein Synthesis Pt 2)

The process by which mRNA is translated into a protein. It has 3 main steps:

1. Initiation: 

   • The ribosome attaches to the mRNA at a start codon (AUG), which codes for methionine (the first amino acid). 

2. Elongation: 

   • Transfer RNA (tRNA) molecules bring amino acids to the ribosome. 

   • Each tRNA has an anticodon that matches a codon on the mRNA. 

   • The ribosome links the amino acids together in the correct order, forming a polypeptide chain (a growing protein). 

   🔹 Example: If mRNA has AUG GCU UAC, the ribosome reads it as: 

   • AUG (Start → Methionine) 

   • GCU (Alanine) 

   • UAC (Tyrosine) 

3. Termination: 

   • When the ribosome reaches a stop codon (UAA, UAG, or UGA), translation stops. 

   • The new protein is released and folds into its proper shape 

The ribosome is a chef, reading the mRNA recipe and using ingredients (amino acids) to make a dish (protein). 

What is RNA Processing?

The modifications made to mRNA before it exits the nucleus, including removal of introns and adding a 5' cap and poly-A tail.

What is meant by the genetic code?

The genetic code is a set of rules that determines how a sequence of nucleotide bases in DNA or RNA is translated into amino acids to build proteins. It acts like a "language" that cells use to read genetic information and make proteins.

Structure of the Genetic Code

✅ Codons: The genetic code is read in triplets called codons. Each codon is a sequence of 3 RNA nucleotides that codes for a specific amino acid.

✅ 4 RNA bases:

• A (Adenine)

• U (Uracil) (in RNA, replaces T in DNA)

• C (Cytosine)

• G (Guanine)

✅ 64 Codons in Total:

• 61 codons code for 20 different amino acids.

• 3 codons are stop codons, signaling the end of translation.

The Genetic Code in Protein Synthesis

Step 1: Transcription (DNA → mRNA)

• DNA sequence: TAC-GGC-AAA

• mRNA codons: AUG-CCG-UUU

Step 2: Translation (mRNA → Protein)

• AUG → Methionine (Start)

• CCG → Proline

• UUU → Phenylalanine

What are ribosomes?

Cellular structures responsible for protein synthesis, found in the cytoplasm and rough endoplasmic reticulum.

What are Exons?

Coding regions of a gene that are expressed in the final protein.

What are Introns?

Non-coding regions of a gene that are removed during RNA processing.

What is the Cell Cycle?

The series of steps a cell goes through to grow, prepare for division, and divide into two daughter cells.  

• Ensures that cells develop properly, repair damage, and replace old or dead cells. 

What is the difference between Mitosis & Meiosis?

Mitosis is the process of nuclear division where replicated chromosomes are separated into two new nuclei for growth and repair, whereas meiosis is cell division for sexual reproduction, producing four genetically unique haploid gametes

What is Interphase?

When the cell grows in preparation for mitosis, makes proteins, and duplicates its DNA.  

It has three phases: 

G₁ Phase (Growth 1)  

• The cell grows and carries out its normal metabolic functions. 

• It makes proteins and organelles & duplicates organelles & cytosolic components   

S Phase (Synthesis) 

• The cell copies its DNA so that each new cell will have a full set of genetic material => DNA & histones synthesised 

G₂ Phase (Growth 2) 

• The cell continues growing and prepares for division 

• Completion of centriole replication  

• Protein synthesis  

• Ensures DNA was copied correctly, ready for M phase  

📌 At the end of interphase, the cell has doubled its DNA and is ready to divide. 

What is the M-phase?

• This is where the nucleus divides, ensuring that each new cell gets an identical set of DNA. 

  • It has 4 stages:  

1. Prophase – DNA condenses into chromosomes, spindle fibres form.  

• Centrosome divides; centrioles migrate to poles.  

• Nuclear envelope disappears  

2. Metaphase – Chromosomes line up in the middle of the cell. 

3. Anaphase – Chromosomes are pulled apart to opposite sides. 

4. Telophase – Two new nuclei form. 

• Nuclear envelope reforms  

• Chromosomes uncoil  

5. Cytokinesis (Final Division of the Cell) 

• The cytoplasm splits, forming two identical daughter cells. 

• In animal cells, the membrane pinches in. 

• In plant cells, a cell plate forms between the two new cells. 

What is the difference between Apoptosis & Necrosis?

Apoptosis - the process of programmed cell death.

Necrosis - accidental, often inflammatory cell death due to external factors

Describe what is meant by a trait and a trait variant

What is an Allele?

Different versions of a gene that may result in different traits.

What is meant by Dominant?

An allele that expresses its trait even in the presence of a recessive allele.

What is meant by Recessive?

An allele that expresses its trait only when two copies are present.

What is a Genotype?

The genetic makeup of an organism; the combination of alleles.

What is a Phenotype?

The observable traits of an organism, resulting from the genotype.

What is meant by Homozygous?

Having two identical alleles for a specific gene.

What is meant by Heterozygous?

Having two different alleles for a specific gene.

What is a Diploid?

A cell with two sets of chromosomes, one from each parent.

What is a Haploid?

A cell with a single set of unpaired chromosomes.

What is an Autosome?

Any chromosome that is not a sex chromosome.

What is a Sex Chromosome?

Chromosomes that determine the sex of an individual (X and Y chromosomes in humans).

What is a Karyotype?

The number and appearance of chromosomes in the nucleus of a cell.

What is a Homologous Chromosome?

Chromosome pairs of the same type, one inherited from each parent.

What is Mendel's Law of Segregation?

The principle that allele pairs separate during the formation of gametes.

Meiosis: Occurs in Anaphase I of Meiosis when homologous chromosomes (each carrying an allele) separate into different gametes.

• This ensures that each gamete (sperm or egg) gets only one allele from a gene pair.

Gene variation: Explains why offspring receive one allele from each parent.

Heritability: Prevents blending inheritance and ensures heritable variation.

What is Mendel's Law of Independent Assortment?

The principle that genes for different traits segregate independently of one another.

Meiosis: Occurs in Metaphase I of Meiosis, when homologous chromosomes randomly align at the metaphase plate.

• The way one pair of chromosomes separates does not influence how another pair separates.

Gene variation: Increases genetic variation by creating new combinations of traits.

Heritability: Explains why siblings look different even if they share the same parents.

✔ Mendel’s Laws explain why inheritance is predictable but still allows for genetic variation.
✔ Meiosis ensures that genes segregate and assort independently, leading to diversity in offspring.
✔ Genetic variation is essential for evolution and adaptation in populations.