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Parent DNA

Original strand of DNA


Daughter DNA

2 new replicated strands


Origins of replication

Site where DNA replication begins


DNA polymerase

Enzyme that assists with DNA replication.


Steps of DNA replication

1. Double helix unwinds, 2 strands separate
2. DNA polymerase lines up nucleotides to form 2 new second strands. Nucleotides line up according to base pairing rules.
3. Hydrogen bonds form between base pairs, forming new rungs. Sugar-phosphate components bond to form sides of the ladder.
4. The new double stranded molecules twist into double helixes.
Occurs in the nucleus



Each DNA strand acts as a template for the formation of a new complementary strand. Nucleotide bases direct the construction of a complementary strand.


Somatic cell

Non-sex cell


How many chromosomes does a somatic cell have?

Each has 23 pairs, 46 in total.



A cell with 2 sets of chromosomes, like a human cell.


Homologous Chromosomes

1. Each person gets 23 chromosomes from one parent and 23 from the other. The 1st, 2nd, etc from each form a homologous pair.
2. These chromosomes are not identical



Portion of DNA that carry protein instructions.


What do chromosomes do?

1. DNA carries instructions for making proteins or creating amino acids. Enzymes can create everything else necessary for the cell.



Going from DNA to RNA



1. Going from RNA to proteins
2. Occurs in the cytoplasm
3. RNA must leave nucleus and enter cytoplasm for translation to occur.


RNA transcription

1. DNA molecule unwinds
2. RNA polymerase creates a complementary strand of RNA, using one strand of DNA and base pairing rules
Occurs in the nucleus


In RNA transcription, do DNA and RNA bond together?

No, RNA is a single stranded molecule. RNA is released and DNA rejoins its complementary partner.


How much of a DNA molecule is used to make RNA?

Only a small portion. Only the genes that correspond to the proteins needed by the cell are used.


Messenger RNA (mRNA)

RNA that actually carries information for protein synthesis (in the form of a nucleotide sequence) from DNA in the nucleus to ribosomes in the cytoplasm.


Ribosomal RNA (rRNA)

Interacts with the cell's ribosomes to make them functional. Ribosomes are made of rRNA and protein


Transfer RNA (tRNA)

1. Carries amino acids from cytoplasm to ribosomes during protein synthesis.



Sequence of 3 nucleotides, which correspond to one amino acid in translation. Order of codons on mRNA specifies the order of amino acids on a protein. Read in a nonoverlapping sequence.


Which are the start and stop codons?

1. Start is the first on all mRNA. AUG (methionine)
2. Stop: UAA, UGA, UAG


tRNA structure

Has a clover leaf shape. An anticodon is contained in the anticodon loop at one end.



Region on tRNA molecule that can base pair with codons on mRNA. Must be complementary.
Example: codon is AUG, anticodon must be UAC


Amino acid attachment site

At the other end of tRNA, an amino acid can attach. The amino acid corresponds with the codon that the tRNA anticodon can base pair with. mRNA codon and tRNA anticodon are like base pairs and have the same amino acid attached.


Binding sites on a ribosome

1. P-site: peptide site where the peptide is attached to the ribosome
2. A-site: amino acid site where the next amino acid is added to the growing protein.
3. mRNA binds to the ribosome so the first codon is the P-site and the second is the A-site.


Translation Steps

1. mRNA binds to ribosome P-site and A-site
2. tRNA, carrying amino acids, base pairs with codons on mRNA.
3. Ribosome forms a peptide bond between the 2 amino acids.
4. The first tRNA, now empty, is released to the cytoplasm and can bind another amino acid
5. The ribosome slides down one codon, so that the codon that was in the A site shifts to the P site, and the next codon in sequence moves to the A site
6. The sequence of steps is repeated until every codon has been base paired and are considered translated.
7. When a stop codon appears in the A-site, the final tRNA is released and the transaction is complete.