Genetics - DNA Structure & Genes Flashcards
What is DNA?
deoxyribonucleic acid
complex macromolecule that contains biological codes to that make each species unique (codes proteins)
genetically inherited
What is the central dogma of genetics?
DNA codes proteins:
DNA (genes) undergoes transcription in the nucleus, turning into RNA (message) that undergoes translation in the cytoplasm to produce a polypeptide
ribosomes assist in producing polypeptides in cytoplasm
mRNA (messenger RNA) is a message from nucleus to ribosomes wt instruction on how to make polypeptides
genetic code is the sequence of bases on mRNA - tells ribosomes which amino acids to use
What is the DNA structure?
double helix molecule - 2 long antiparallel strands
each strand made of single units called nucleotides linked by hydrogen bonding btw complementary base pairs
millions of base pairs / strand coiled wtin nucleus to make chromosomes
What are the components of the single monomer / subunit nucleotide?
join together to form polynucleotide chains
- pentose sugar (5 carbons: deoxyribose / ribose)
- phosphate group
- nitrogenous base
What are the types of nitrogenous bases?
Purines - 2 ring structure
- Adenine
- Guanine
Pyrimidines - 1 ring structure
- Thymine
- Cytosine
- Uracil (replaces thymine in RNA)
What are the complementary base pairs and how are they bonded?
Chargaff’s rule - purine + pyrimidine
- Adenin & Thymine / Uracil - 2 hydrogen bonds
- Guanine & Cytosine - 3 hydrogen bonds
How are hydrogen bonds involved in DNA?
the hydrogen bond repelling forces provide the DNA molecule wt twisted helix structure
Where are the phosphate group and nitrogenous base attached to on the pentose sugar?
first count and label carbons in pentose sugar - count clockwise from the oxygen, labelling 1’, 2’, 3’, 4’, 5’
5’C - phosphate group
1’C - nitrogenous base
How are polynucleotide chains formed?
nucleotides form covalent bonds btw the pentose sugar (deoxyribose) and phosphate group to form a polynucleotide chain
complementary bases pair up due to hydrogen bonds = double stranded
strands align antiparallel (5’ to 3’ - where covalent bond is) - 5’ end wt phosphate group, 3’ nitrogenous base is free
the double stranded molecule then twists to form double helical structure
bases in the inside as very reactive
phosphate group and deoxyribose form backbone as they are hydrophilic
hydrogen bonds also hold adjacent sections of DNA together
How is DNA read?
read in triplets (3 bases)
each triplet sends instructions to cell to :
- switch genes on / off
- make proteins
- make enzymes
What is the Watson and Crick DNA model?
British scientists
1952 correctly proposed structural organisation of DNA
efforts guided by molecular distance and bond angles, developed by Linus Pauling
also based on:
1919 Phoebus Levene - DNA composed of nucleotides
1950 Erwin Chargaff - DNA composed of equal # of purines and pyrimidines
1953 Rosalin Franklin - Helical structure
Trial and error discovered:
DNA strands are antiparallel & helical
DNA pairs through complimentary bases
Outer edges of bases remain exposed to allow access to replicative and transcriptional proteins
won noble prize
What is RNA?
ribonucleic acid
more versatile single stranded nucleic acid form that functions to transfer genetic instructions from the nucleus to cyctoplasm
What is the structural difference btw deoxyribose and ribose sugars?
deoxyribose has H and ribose has OH
What are the types of RNA and their functions?
mRNA (messenger) - transcript copy of gene (encodes specific polypeptide)
tRNA (transfer RNA) - carries polypeptide subunits (amino acids) to organelles responsible for synthesis (ribosomes)
rRNA (ribosomal RNA) - primary component of ribosome & responsible for its catalytic activity
What are genes?
heritable factor that controls a specific characteristic, consisting of a length of DNA occupying a particular position on a chromosome (locus)
