Genetics Test Paletzki 3-11-25

genetics

the science that studies how characteristics get passed from parent to offspring

DNA

the molecule that stores genetic information, deoxyribonucleic acid

DNA is composed of

a string of nucleotides

nucleotides are made up of 3 parts

a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogen base

What does DNA look like?

the shape looks like a twisted ladder, and the sides of the ladder are composed of alternating deoxyribose sugar and phosphate groups, commonly called the “sugar phosphate backbone” the rungs of the ladder are made of nitrogen bases

Edwin Chargaff

determined that the amounts of adenine and thymine were equal and the amounts of cytosine and guanine were equal (in part due to chargaff, we now know that all organisms use the same genetic code)

Adenine =

thymine for DNA, uracil for RNA

cytosine =

guanine

rosalind franklin

used crystallography x-rays to show that 2 DNA strands were twisted

francis crick and james watson

used franklin’s picture to make the first correct model of the double helix

we call the 2 DNA strands

complementary

gene

a segment of DNA that codes for a protein, causing genetic characteristics or traits

because DNA contains the code for creating traits it must…

be accurately transferred from parents to offspring, and with cells constantly growing and dividing it must be accomplished without breaking the DNA strands

how is DNA protected

it is tightly coiled around proteins called histones and condensed into chromosomes

nucleosome

a histone + the DNA wrapped around it

DNA replication

duplicates genetic information prior to cellular division

helicase

an enzyme that “unzips” the two strands of DNA

DNA polymerase

an enzyme that brings nucleotides to match one of the strands (known as the parent strand)

the new DNA strand in replication is known as the

daughter strand

the new sequence (will/won’t) match the old sequence because of

WILL, because of strict base pairing rules

semi-conservative

only half of each parent strand remains in the new DNA molecule

role of enzymes overall in replication

separating the two strands and using one side as the blueprint to make a complementary strand

RNA

the other type of nucleic acid found in cells, required to make proteins from the DNA double helix

ways RNA differs from DNA

single-stranded, ribose sugars, uracil instead of thymine

what does mRNA stand for

Messenger RNA

what does rRNA stand for

Ribosomal RNA

tRNA

transfer RNA

amino acids

building blocks of proteins

DNA remains__ in the cell’s __ except during cell division

trapped, nucleus

role of mRNA

make a copy of the DNA sequence so the message can leave the nucleus without endangering the original genetic blueprint

transcription

the process of making an mRNA copy from a DNA template in called transcription

what happens during transcription

an enzyme called RNA polymerase unwinds a small section of the DNA strand, then uses one side of the double helix as a template to make an mRNA copy

how does RNA copy specific genes

by finding promoter sequences at the beginning of each gene

what portion of the mRNA is used

not all of the newly created mRNA is required to code for a protein, some mRNA is spliced out because it is unnecessary for that gene

mRNA carries the genetic message from the__ in the___ to the ___

DNA, nucleus, cytoplasm

the cytoplasm contains

ribosomes, which use the mRNA to make proteins

codon

3 bases

role of tRNA

molecules like matchmakers, they match a codon to an amino acid

the codon is recognized by

an anticodon on the tRNA molecule, in this way, the cell accurately brings in exactly the amino acids that are coded for the DNA sequence

stop codons

signify the end of an mRNA sequence for one gene, UAA, UAG, and UGA

AUG

a start codon that signifies the start of the next gene, and if found in the middle of a sequence it codes for the amino acid methionine

translation

an mRNA message is turned into an amino acid chain

translation occurs in the

ribosomes of the cell

role of ribosomes in translation

the ribosome attaches at the start codon and continues to move down the mRNA, bringing in tRNA molecules to create an amino acid chain until it reaches a stop codon

role of amino acids in translation

as tRNA molecules bring in amino acids to match with the mRNA codons, their amino acids bond together creating a long string

amino acids are bonded with

peptide bonds, so the resulting chain is called a polypeptide chain, and the chain will ultimately fold into a protein to be used by the cell

gene regulation

rather than producing unnecessary proteins, cells control which genes are used

how do prokaryotes regulate gene expressions

bacteria like e.coli can turn transcription on or off with a group of genes called an operon

how do eukaryotes regulate gene expression

in eukaryotes, the RNA polymerase does not bind directly to the promoter, it is assisted by a set of specialized proteins known as transcription factors

transcription factors

can cause certain genes to relax, allowing transcription. they can also cause the DNA to coil very tightly, blocking the RNA polymerase

mutation

when DNA is not copied correctly

DNA mutations come in two forms:

point mutations + frameshift mutations

point mutation

caused by a mistake in base pairing for one nucleotide

frameshift mutation

a nucleotide is inserted or deleted causing the whole polypeptide chain to be disrupted

4 types of chromosomal mutations

deletion, duplication, inversion, and translocation

deletion chromosomal mutations

a portion of a chromosome is deleted

duplication chromosomal mutations

a portion of a chromosome is repeated

inversion chromosomal mutations

a portion of a chromosome is flipped

translocation chromosomal mutations

a portion of one chromosome is added to a different chromosome

how do mutations occur

some are simply mistakes in DNA replication or transcription, but mutagens can cause mutations artificially

mutagens

anything that causes a mutation (ex. radioactive substances, certain chemicals, x-rays)

chromosomal mutations involve mistakes in

whole sections of chromosomes