Cell Types and DNA Structure

Cell Types and DNA

• Two basic cell types exist: Prokaryotes and Eukaryotes
• Prokaryotes (e.g., bacteria) are smaller (approximately 1 micrometer), with a single circular DNA molecule located in the nucleoid region. They lack membrane-bound organelles.
• Eukaryotes (e.g., plants, animals) are larger (10-100 micrometers), with linear DNA organized into chromosomes located in the nucleus. They possess membrane-bound organelles.

DNA Structure and Function

• DNA (deoxyribonucleic acid) is a macromolecule found in all living cells, controlling cellular processes.
• It's composed of a double helix.
• DNA has a sugar-phosphate backbone with bases (adenine, thymine, cytosine, and guanine) pairing up – adenine with thymine, and cytosine with guanine.

DNA Discovery

• Friedrich Miescher isolated DNA in 1859.
• James Watson and Francis Crick proposed the double helix model in the early 1950s.

DNA Replication

• DNA replication is semi-conservative, creating two identical DNA molecules from one original molecule.
• Enzymes like helicase unzip the DNA, and DNA polymerase adds complementary bases.
• The process involves the separation of DNA strands and the creation of new complementary strands.

Chromosomes and DNA Location

• Chromosomes are structures that organize DNA within a cell.
• DNA is packaged into chromosomes.
• Prokaryotic chromosomes are usually circular.
• Eukaryotic chromosomes are linear and found in the nucleus.
• Telomeres are protective caps on the ends of chromosomes.

DNA in Eukaryotes

• Eukaryotes have multiple linear chromosomes in their nucleus, and DNA is associated with proteins (histones).
• Extra-nuclear DNA is also found in mitochondria and chloroplasts.

Macromolecules

• Large molecules within organisms are macromolecules.
• Four major groups exist: carbohydrates, proteins, lipids, and nucleic acids.

Genes and Protein Synthesis

• Genes are segments of DNA that code for specific proteins or RNA molecules.
• Protein synthesis involves two main processes: transcription and translation.
• Transcription produces a messenger RNA (mRNA) molecule, which carries the genetic code from the DNA.
• Translation uses the mRNA code to assemble amino acids into a protein.

Protein Synthesis Stages

• Transcription occurs in the nucleus, where DNA is copied to RNA.
• RNA polymerase separates the DNA strands, and free nucleotides match bases on the DNA strand.
• mRNA moves to the cytoplasm.
• Translation happens in the cytoplasm; tRNA carries amino acids to the ribosome.
• A polypeptide chain is produced based on the mRNA sequence of codons.

RNA Structure and Types

• RNA (ribonucleic acid) is single-stranded and uses uracil instead of thymine.
• mRNA carries genetic information from DNA to ribosomes.
• tRNA brings amino acids to the ribosomes in translation.
• rRNA is a component of ribosomes, enabling protein synthesis.

Introns and Exons

• DNA includes exons (coding regions translated into proteins) and introns (non-coding regions removed).
• These regions are located in a gene.
• Introns get removed after transcripiton to form functional mRNA.

Ribosomes and Translation

• Ribosomes are made of rRNA and proteins, and are the site of protein synthesis.
• tRNA carries amino acids to ribosomes, and the mRNA sequence determines the amino acid sequence in the protein chain.

Transcription and DNA Replication

• Transcription and Replication are crucial for cell function.
• DNA is transcribed into an mRNA molecule, which is then translated to a polypeptide chain.
• DNA is replicated creating an identical copy needed for cell division.

DNA Replication Process

• Helicase unzips the DNA double helix, breaking hydrogen bonds.
• Free nucleotides pair with complimentary bases on the template strands
• Polymerases join nucleotides to produce new DNA strands.
• DNA ligase joins fragments, resulting in continuous DNA strands.

DNA Replication Enzymes

• Several enzymes are involved in the process, including helicase, polymerase, and ligase.

Telomeres and DNA Replication Limitations

• Telomeres are the protective caps on chromosomes.
• Telomeres shorten with each replication.
• Shortened telomeres eventually cause the death of cells.

Important Definitions

• Define Key terms such as: deoxyribonucleic acid, ribonucleic acid, transcription, replication, translation, genes, chromosomes, exon, intron, codon, amino acid, polypeptide, histones, nucleotides, RNA, mRNA, and tRNA.

Explore the fundamentals of cell types and the intricate structure of DNA in this quiz. Learn about the differences between prokaryotes and eukaryotes, as well as the history and function of DNA. Test your knowledge on DNA replication and the pivotal discoveries in genetics.