Biology 6.1 Flashcards
(81 cards)
Central dogma of Biology
Genetic information is encoded as DNA via nucleotides, then transcribed to RNA which can be translated to proteins
Nucleotides
Basic unit for genetic information, linked by phosphodiester bonds. Nitrogenous bases adenine, guanine, uracil, thymine and cytosine. Sugar is ribose or deoxyribose. Has phosphate
Deoxyribonucleic acid (DNA)
2 nucleotide polymers hydrogen bonded together in anti-parallel, right-handed helix, with each nucleotide strand having a 5’ and 3’ end. G with C. A with T.
Ribonucleic acid (RNA)
Synthesized upon transcription from DNA. Single polymer strand. mRNA, tRNA, rRNA. G with C. A with U.
Start codon
AUG, methionine
Stop codons
UAA, UGA, UAG, no specific amino acid from these
mRNA
Transcribed from DNA that encodes a protein product, then transported to cytoplasm where it is translated to a protein using ribosome. mRNA encodes sequence of polypeptide via codons where 3 nucleotides of mRNA encodes on amino acid
tRNA
Delivers amino acid to ribosome via its cloverleaf shape. Has anticodon that pairs with codon of mRNA, allowing tRNA to bind to ribosome to allow transported amino acid to join polypeptide chain. During anticodon and codon base pairing, the third nucleotide is called wobble pair and may not match exactly for the pairing to occur
rRNA
Globular protein that is major component of ribosome structure. 2 types of rRNA are transcribed in the nucle jolus of the nucleus where it combines with other proteins to be assembled to the large and small units of the ribosome
Semi-conservative
In interphase, DNA is unzipped and single-stranded binding proteins maintain the separation to allow both parental strands to act as template for new strands. Thus, new DNA helices have one parental and one new strand
DNA Replication step 1/5
DNA is unwound at origin of replication using helicase enzyme to break hydrogen bonds between bases and create Y-shaped replication fork where unwinding and synthesis occurs
DNA Replication step 2/5
At 3’ end of single strand, primate enzyme adds RNA primer that DNA polymerase uses to start DNA synthesis.
DNA Replication step 3/5
DNA polymerase adds new DNA nucleotides in a semi-conservative manner by reading parent strand in 3’ to 5’ direction. For mistakes, DNA polymerase proofreads by backtracking to remove the mistake and replace it with the correct sequence. Since DNA is bidirectional, DNA synthesis occurs differently for each parent strand.
DNA synthesis for leading strand
Uses template 3’ to 5’. Replication is continues, synthesis occurs down the replication fork while placing new nucleotides down in a 5’ to 3’ direction.
DNA synthesis for lagging strand
Uses template 5’ to 3’. Primase sets down small fragments of the RNA primer in several regions along lagging strand to allow synthesis of Okazaki fragments, later sealed together with DNA ligase
DNA Replication step 4/5
Unwinding DNA causes torsion on areas still hydrogen bonded, topoisomerase enzymes prevent knots by breaking and rejoining the double helix, helping to reduce torsion
DNA Replication step 5/5
DNA synthesis ends at termination sites
Telomere replication
End of lagging strand has section that cannot be replicated, causing chromosomes to shorten every cycle of DNA replication and deletion of important sequences. Thus each linear chromosome has telomere, region of repeated sequences, at the ends that get shortened in place of genes. In some cells, telomerase enzyme attaches to end of template stand to add a DNA primer that can be extended by DNA polymerase, however, not many cells can do this and enter senescence when telomeres become short. Hayflick Limit explains how telomere shortening is correlated with aging
Prokaryotic vs eukaryotic DNA replication
Eukaryotes have multiple origins of replication that eventually connect and result in production of 2 separate linear semi-conservative strands. Bacteria only has one origin of replication. Eukaryotic chromosomes are linear, resulting in DNA loss at ends (telomere) of lagging strand. Bacterial strand is circular
Transcription step 1/4
Initiation: DNA has promoter region called TATA Box that RNA polymerase attaches to to unzip the DNA to 2 strands. One strand acts as the template strand called non-coding because it has opposite sequence as mRNA. Template strand is read by RNA polymerase to make mRNA. The second strand is the non-template strand called coding because it has the same sequence as mRNA but T instead of U. Non-template strand is not read by RNA polymerase
What does RNA Polymerase I, II, and III make?
RNA polymerase I makes rRNA. RNA polymerase II makes mRNA. RNA polymerase III makes tRNA.
Transcription step 2/4
Elongation: RNA polymerase unzips DNA and adds RNA nucleotides using the DNA template strand which is read 3’ to 5’. New RNA strand is made 5’ to 3’ The new strand is pre-mRNA, made from only one DNA strand
Transcription step 3/4
Termination: RNA polymerase eventually meets series of repeating sequences of nucleotides (AAAAA… in eukaryotes) called termination point
Transcription step 4/4
In bacteria, RNA transcripts are mature mRNAs and can be directly translated after transcription. In eukaryotes, pre-mRNA needs to be altered before becoming mature mRNA and leaving the nucleus. This consists of 5’ cap, 3’ Poly-A tail and splicing
