DNA Structure and Function

DNA Nucleotide

• A subunit of DNA, consisting of a deoxyribose sugar, a phosphate group, & a nitrogenous base
• The nitrogenous bases are Adenine (A), Thymine (T), Guanine (G), and Cytosine (C)
• They are linked together in long chains called DNA strands

DNA Strand

• A chain of linked DNA nucleotides
• They run in opposite directions (antiparallel)

DNA Molecule (Double Helix)

• Two DNA strands twisted together
• Joined by hydrogen bonds between complementary base pairs
  • Adenine pairs with Thymine (A-T)
  • Guanine pairs with Cytosine (G-C)

Antiparallel DNA Molecule

• Two DNA strands run in opposite directions
• One strand runs from 5' to 3'
• The other runs from 3' to 5'

DNA Sequence

• The order of nitrogenous bases in a DNA strand
• A, T, C, G are used to represent the bases
• The sequence holds genetic information

Histone

• Proteins that DNA wraps around
• They help compact DNA in chromosomes

Chromosome Packaging

• The process of organizing DNA within chromosomes
• DNA is tightly coiled using histones to fit into the nucleus

Chromosome (Unreplicated)

• One long piece of DNA containing genes
• Found in the nucleus of eukaryotic cells
• Consists of a single strand of tightly packed DNA

Chromosome (Replicated)

• Contains two identical sister chromatids
• The sister chromatids are held together by a centromere
• Replicated chromosome is ready for cell division

Telomere

• Protective caps at the ends of chromosomes
• They prevent the ends of chromosomes from being degraded or sticking together

Centromere

• Region of a chromosome that connects the sister chromatids together
• It plays a crucial role in chromosome segregation during cell division

Gene

• A segment of DNA that codes for a specific protein or RNA molecule
• It is the functional unit of heredity

DNA Template Strand

• The strand of DNA that is used as a template for RNA synthesis
• It is read by RNA polymerase to create a complementary RNA molecule

Gene Locus (Loci pl.)

• The specific location of a gene on a chromosome

Allele

• One of two or more alternate forms of a gene
• Different alleles can produce different traits

Homozygous Genotype

• Two identical alleles for a gene
• Example: AA or aa

Heterozygous Genotype

• Two different alleles for a gene
• Example: Aa

Sister Chromatids

• Two identical copies of a chromosome
• They are linked together at the centromere until cell division

Homologous Chromosomes

• Pair of chromosomes containing the same genes
• One chromosome comes from each parent
• They can have different alleles for the same genes

Non-homologous Chromosomes

• Chromosomes that do not contain the same genes
• They are not paired up during meiosis

Diploid Cell

• Cell with two sets of chromosomes
• One set from each parent

Haploid Cell

• Cell with one set of chromosomes
• Example: Gametes (sperm and egg cells)

RNA Nucleotide

• Similar to DNA nucleotides, but with a ribose sugar and uracil (U) instead of thymine (T)
• The nitrogenous bases are adenine (A), uracil (U), guanine (G), and cytosine (C)

Protein

• Complex molecules made of amino acids
• They perform a variety of functions in the body, including structural support, catalysis, transport, and signaling

Amino Acid

• The building blocks of proteins
• There are 20 different amino acids that can be combined in various sequences to form different proteins

Protein Synthesis

• When an amino acid chain builds a protein using genetic instructions
• It involves two steps: transcription and translation

Transcription

• The process of copying a gene's DNA sequence into RNA
• It involves the use of an enzyme called RNA polymerase

Transcription (Steps)

• RNA polymerase binds to a promoter site on the DNA
• RNA polymerase unwinds the DNA and reads the template strand
• RNA polymerase uses the DNA template to create a pre-mRNA molecule
• Pre-mRNA molecule is a complementary copy of the DNA template strand

Translation

• The process of using the mRNA code to build a protein
• It involves the use of ribosomes and transfer RNA (tRNA)

Translation (Steps)

• mRNA codons (3-base sequences) bind to complementary tRNA anticodons
• Each tRNA molecule carries a specific amino acid
• Ribosomes join the amino acids together to form a polypeptide chain
• The polypeptide chain folds into a specific three-dimensional structure, forming a protein