Cell Nucleus, DNA, and RNA

• DNA is likened to a computer program, but far more advanced
• DNA is indifferent; life adapts to its characteristics

The Nucleus

• The nucleus serves as the control center within eukaryotic cells
• It dictates and regulates all cellular activities
• Instructions for cellular activities are carried in molecules of DNA within the nucleus
• DNA is an organism's genetic information
• Genetic information is the main instructions, determining a cell's identity, function, growth, division, and lifespan
• The nuclear membrane regulates the transit of substances between the nucleus and the cytoplasm

The Nucleolus

• The nucleolus is a large structure inside the nucleus
• Ribosomes, crucial for protein synthesis, are produced here
• Ribosomes facilitate protein synthesis, where proteins are synthesized in the cell

DNA & RNA

• DNA is deoxyribonucleic acid
• DNA stores genetic material, passing it from one generation to the next during reproduction
• RNA is ribonucleic acid
• RNA transmits DNA's instructions, specifying the amino acid sequence for protein synthesis, out of the nucleus

Structure of DNA & RNA

• Both DNA and RNA are composed of nucleotides
• Nucleotides consist of a 5-carbon sugar (pentose)
  • The sugar in DNA is deoxyribose
  • The sugar in RNA is ribose
• Nucleotides also include a:
  • Phosphate group
  • Nitrogenous base

Structure of DNA

• There are four kinds of nitrogenous bases in DNA:
  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)
• DNA structure is a long, two-stranded molecule forming a spiral ladder, known as a double helix
• The sides of the DNA ladder comprise sugar (deoxyribose) and phosphate, forming the sugar-phosphate backbone
• The steps of the DNA ladder consist of paired nitrogenous bases
• These pairs fit together like puzzle pieces, referred to as complementary base pairs
• The bases in DNA join in a specific way, known as the base-pair rule:
  • Adenine (A) pairs with Thymine (T)
  • Cytosine (C) pairs with Guanine (G)
• The two strands of the DNA double helix are held together by hydrogen bonds between the paired bases

Structure of RNA

• RNA is single-stranded and is made through complementary base pairing with a DNA strand, which servers as a template
  • RNA nucleotides contain ribose (not deoxyribose)
  • Uracil (U) replaces thymine (T) in RNA, but the other three bases (A, C, G) are the same as in DNA
• Three types of RNA include:
  • Messenger RNA (mRNA)
  • Transfer RNA (tRNA)
  • Ribosomal RNA (rRNA)

Chromatin and Chromosomes

• DNA molecules in the nucleus usually exist in the form of chromatin
• As a eukaryotic cell prepares to divide, chromatin strands coil into compact chromosomes with an X shape
• DNA molecules in the nucleus are organized in pairs, referred to as homologous chromosomes
• Organisms possess different numbers of chromosomes, a constant number within a species
• Human cells have 46 chromosomes (23 pairs)
• Mosquito cells have 6 chromosomes (3 pairs)
• Dog cells have 78 chromosomes (39 pairs)
• Garden pea cells have 14 chromosomes (7 pairs)

Genes

• Genes are small DNA segments located at specific positions on a chromosome
• Genes carry the instructions to make proteins
• Human DNA molecules (chromosomes) contain roughly 1,000 genes allowing for the production of 1,000 types of proteins
• The human genome has around 20,000-25,000 genes
• Each gene has a specific sequence of nucleotides along the DNA "ladder," varying with its length

Proteins

• Proteins are molecules required by all body cells to function correctly
• Every cell in the body shares the same amount of genetic information, but only specific genes are activated in certain cells to produce specialized proteins