BIO 110 Module 9: DNA Structure and Gene Expression

what is a nucleotide made up of?

a sugar, a phosphate group, and a base

what is the structure of DNA?

double helix polymer made up of repeating nucleotides bound covalently, and linked by phosphodiester bonds

hydrogen bonds

connect complementary DNA strands (A, T, G, C)

pyrimidines

cytosine and thymine

purines

guanine and adenine

how many chromosomes are in eukaryotic cells?

multiple

how many chromosomes are in prokaryotic cells?

one circular chromosome

where are chromosomes located in eukaryotic cells?

the nucleus

where are chromosomes located in prokaryotic cells?

the nucleoid

the two strands of DNA are ___

complementary, meaning the sequences of bases on one strand can be used to create the correct sequence of bases in the other strand

semiconservative replication

produces two new copies of double stranded DNA that each contain one of the original strands of DNA and one new strand

what are the main stages of DNA replication?

initiation, elongation, termination

replication fork

region where a cell’s double helix DNA has been unwound and separated to create an area for replication

helicase

enzymes that “unzip the DNA” and separate the two strands of the double helix to allow access for other enzymes involved in DNA replication

RNA primer

RNA molecules that are used to initiate DNA synthesis during replication

DNA polymerase (DNAP)

type of enzyme that create DNA molecules by assembling nucleotides

okazaki fragments

short, newly made DNA fragments that are formed on the lagging template strand during DNA replication

what is the leading strand?

the DNA strand that runs in the 5’ to 3’ direction in the replication fork; it is made as a continuous piece

what is the lagging strand?

the DNA strand that runs in the 3’ to 5’ direction towards the replication fork, also holds okazaki fragments

DNA ligases

enzymes needed for DNA repair, replication, and recombination

mistakes during replication are detected and repaired by ___

DNA polymerase

mismatch repair

functions to correct replication errors in newly made DNA, and to prevent recombination between related, but not identical DNA sequences

nucleotide excision repair (NER)

removes lesions on the DNA caused by UV radiation or chemical damage

uncorrected replication errors result in ___

mutations

what are three different categories of mutations?

point, frameshift, and chromosome

what is telomerase?

an enzyme in cells that helps keep them alive by adding DNA to telomeres (the ends of chromosomes)

what does transcription do?

converts DNA into messenger RNA (mRNA)

what does translation do?

decodes mRNA into amino acids

where does transcription occur?

in the nucleus

where does translation occur?

in the ribosome

what are the three types of RNA?

messenger, ribosomal, and transfer

what does messenger RNA do?

carries protein info from the DNA in the nucleus to the cytoplasm

what does ribosomal RNA do?

decodes amino acids and links them together

what does transfer RNA do?

serves as a link between the messenger RNA and the growing chain of amino acids that make up a protein

what happens during initiation of transcription?

RNA polymerase binds to the promoter region of a gene

what happens during elongation of transcription?

RNA polymerase adds nucleotides to the strand according to the base pairing

what happens during termination of transcription?

RNA polymerase reaches the end of the DNA strand and detaches

elongation occurs at a rate of __ nucleotides per second

40

what happens during initiation of translation?

the first tRNA, mRNA, and ribosome get together

what happens during elongation of translation?

the amino acid chain gets longer

what happens during termination of translation?

a stop codon reaches the ribosome’s A site and mRNA leaves the ribosome

every three bases (a triplet) specifies an __ to be included into a growing polypeptide chain

amino acid

each base triplet in RNA is called a ___

codon

what is the “start” codon?

AUG

eukaryotic gene expression is regulated during ___, ___, and ___

transcription and RNA processing, protein translation, and post-translational modifications of proteins