Concept 3 Unit 4 Flashcards

Front

Nucleotide

Back

A nucleotide is the monomer unit of nucleic acids composed of a sugar (deoxyribose in DNA), a phosphate group, and a nitrogenous base. Nucleotides link together to form DNA or RNA strands and determine genetic information via their base sequence.

Front

Base pairing

Back

Base pairing refers to complementary hydrogen bonding between nitrogenous bases: adenine with thymine (A—T) and cytosine with guanine (C—G) in DNA. These rules ensure accurate matching during DNA replication and transcription.

Front

Double helix

Back

The double helix is the twisted-ladder structure of DNA formed by two antiparallel strands of nucleotides. The sugar-phosphate backbones form the exterior while base pairs form the rungs joined by hydrogen bonds.

Front

Semi-conservative

Back

Semi-conservative replication means each new DNA molecule contains one original (parent) strand and one newly synthesized strand. This mechanism preserves part of the original molecule after replication.

Front

Replication

Back

DNA replication is the process of copying the entire DNA molecule during S phase so that each new cell receives an identical genome. Enzymes unzip the helix and synthesize complementary strands according to base-pairing rules.

Front

Complementary strand

Back

A complementary strand is a newly formed DNA or RNA strand whose base sequence is determined by base-pairing with the template strand. In DNA, the complement of A is T and of C is G; in RNA, A pairs with U instead of T.

Front

mRNA

Back

mRNA (messenger RNA) copies the genetic instructions from DNA during transcription and carries this message to ribosomes in the cytoplasm. It contains codons that specify amino acid sequences during translation.

Front

tRNA

Back

tRNA (transfer RNA) transports specific amino acids to the ribosome and uses an anticodon to base-pair with mRNA codons. Each tRNA matches a particular amino acid, enabling correct polypeptide assembly.

Front

rRNA

Back

rRNA (ribosomal RNA) is a structural and catalytic component of the ribosome and helps facilitate peptide bond formation. Together with proteins, rRNA makes up the ribosomal subunits where translation occurs.

Front

Transcription

Back

Transcription is the process of synthesizing mRNA from a DNA template in the nucleus using complementary base-pairing (with U replacing T). The completed mRNA leaves the nucleus to be translated in the cytoplasm.

Front

Translation

Back

Translation is the ribosomal process that reads mRNA codons and assembles the corresponding amino acids into a polypeptide chain. tRNAs bring amino acids and the ribosome links them with peptide bonds until a stop codon ends synthesis.

Front

Codon

Back

A codon is a triplet of nucleotides on mRNA that specifies a single amino acid or a stop signal during translation. The genetic code maps codons to amino acids universally across most organisms.

Front

Homologous pair

Back

A homologous pair consists of two chromosomes (one from each parent) that carry the same types of genes in the same order, though alleles may differ. Homologs pair during Meiosis I and can exchange segments via crossing over.

Front

Sister chromatids

Back

Sister chromatids are two identical copies of a single chromosome formed by DNA replication and joined at the centromere. They separate during Meiosis II (and mitotic anaphase) to become individual chromosomes.

Front

Diploid

Back

Diploid (2n) describes cells with two full sets of chromosomes, one set from each parent (e.g., human somatic cells with 46 chromosomes). Diploid cells undergo meiosis to produce haploid gametes for sexual reproduction.

Front

Haploid

Back

Haploid (n) cells contain a single set of chromosomes and are the product of meiosis (e.g., human gametes with 23 chromosomes). Fertilization restores diploidy when two haploid gametes fuse.

Front

Crossing over

Back

Crossing over is the exchange of DNA segments between homologous chromosomes during Prophase I of meiosis, producing chromosomes that are genetic mixtures of both parents. This process increases genetic variation among gametes.