Heredity and Continuity of Life: DNA, Genes, and Protein Synthesis

Practice flashcards covering Unit 4: Heredity and continuity of life, specifically focusing on DNA structure, replication, protein synthesis, gene regulation, and mutations.

What is the location and structure of DNA in eukaryotic cells versus prokaryotic cells?

In eukaryotic cells, DNA is a double-stranded molecule bound to histone proteins in chromosomes in the nucleus, or unbound in mitochondria and chloroplasts. In prokaryotes, it occurs as unbound circular DNA in the cytosol.

What are the three core units that make up a DNA nucleotide?

A phosphate group (the backbone), a $5$-carbon sugar called deoxyribose, and a nitrogenous base (adenine, thymine, cytosine, or guanine).

Identify the purines and pyrimidines found in nucleic acids.

Purines, which have a two-ring structure, include Adenine (A) and Guanine (G). Pyrimidines, which have a one-ring structure, include Cytosine (C), Thymine (T) in DNA, and Uracil (U) in RNA.

Describe the base-pairing rules and the type of bonding for DNA strands.

Adenine (A) pairs with Thymine (T) via $2$ weak hydrogen bonds. Guanine (G) pairs with Cytosine (C) via $3$ weak hydrogen bonds.

What are the functions of Helicase and DNA Polymerase during replication?

Helicase unwinds the double helix and separates DNA strands by breaking hydrogen bonds. DNA Polymerase forms the new complementary strands by adding nucleotides in the $5'$ to $3'$ direction.

Compare the synthesis of the leading strand and the lagging strand.

The leading strand is synthesized continuously in the $5'$ to $3'$ direction. The lagging strand is synthesized discontinuously in small segments known as Okazaki fragments.

Define the terms 'gene' and 'genome' according to the lecture notes.

A gene is a region of DNA that contains the information to produce a protein or functional RNA. A genome is the complete set of genetic material in an organism in a haploid set of chromosomes.

Distinguish between introns and exons in a gene sequence.

Exons are the 'coding' portions of a gene that are expressed and kept in the final RNA sequence. Introns are 'noncoding' portions that are removed by RNA splicing prior to the formation of mRNA.

What are the roles of mRNA, tRNA, and rRNA in protein synthesis?

mRNA (messenger) carries a copy of the DNA sequence; tRNA (transfer) carries amino acids to match its anticodon to mRNA codons; rRNA (ribosomal) forms the ribosomes where translation occurs.

What modifications are made to primary RNA during processing?

A $5'$ cap (modified guanosine) is added to the $5'$ end, a poly-A tail (chain of adenines) is added to the $3'$ end, and introns are spliced out.

What is the function of transcription factors?

Transcription factors are proteins or regulatory genes that can block the attachment of RNA polymerase to prevent gene expression or alter the rate at which a gene is expressed.

What is the significance of Hox genes in embryo development?

Hox genes are master regulator genes that control the body plan along the head-to-tail region in embryos, determining where structures like heads or eyes grow.

How is 'epigenetics' defined in the context of gene expression?

Epigenetics is any mechanism that alters gene expression without altering the DNA sequence, such as histone coiling or DNA methylation.

Contrast somatic mutations with germline mutations.

Somatic mutations occur in body cells and affect only the individual. Germline mutations occur in gametes (ova and sperm) and can be inherited by offspring, potentially influencing the gene pool.

Explain the difference between synonymous and non-synonymous point mutations.

Synonymous mutations have no effect on the polypeptide chain because the substituted base results in the same amino acid. Non-synonymous mutations cause an amino acid replacement.

What is the effect of frameshift mutations (insertions and deletions)?

Frameshift mutations change the codon sequence of the mRNA for the entire remainder of the strand, leading to significant changes in the resulting polypeptide chain.

What is aneuploidy and what biological error causes it?

Aneuploidy is the presence of an abnormal number of chromosomes (such as Down syndrome, which is trisomy $21$). It is caused by non-disjunction, the failure of chromosomes to separate correctly during cell division.

What distinguishes a mutagen from a carcinogen?

A mutagen is an agent that causes random changes to DNA. A carcinogen is an agent that directly increases the incidence of cancer, either by damaging DNA or by accelerating uncontrolled cell growth.